Physics Class 10 Short and Long Questions Federal Board Syllabus Important

Complete answers/ solutions including unit number, unit name and questions - according to class 10 physics, FBISE Syllabus

Unit 10: Simple Harmonic Motion and Waves

Important Short Questions:

What are conditions for a body to perform simple harmonic motion?

Conditions for Simple Harmonic Motion:

• A body must experience a restoring force proportional to its displacement from equilibrium.
• The force must always act towards the equilibrium position.
• The magnitude of the force must be directly proportional to the displacement.

What are damped oscillations. How damping progressively reduces the amplitude of oscillation?

Damped Oscillations:

• Damped oscillations occur when the energy of an oscillating system is gradually dissipated by an external force or through internal friction.
• Damping progressively reduces the amplitude of oscillation until the oscillations eventually cease.

Difference between mechanical waves and electromagnetic waves.

Difference between Mechanical Waves and Electromagnetic Waves:

• Mechanical waves require a medium (solid, liquid, or gas) for propagation, while electromagnetic waves can propagate through vacuum (empty space).
• Mechanical waves transfer energy through the motion of particles in the medium, whereas electromagnetic waves consist of oscillating electric and magnetic fields.

Difference between transverse waves and longitudinal waves.

Difference between Transverse Waves and Longitudinal Waves:

• Transverse waves have particle oscillations perpendicular to the direction of wave propagation, while longitudinal waves have particle oscillations parallel to the direction of wave propagation.
• Examples of transverse waves include waves on a string, while examples of longitudinal waves include sound waves.

Define Wave Speed. Derive V= f

Wave Speed Definition and Derivation:

• Wave Speed (v) is the speed at which a wave travels through a medium.
• Derivation of v = fλ:
  • v = λ / T (where λ is the wavelength and T is the time period)
  • But T = 1 / f (where f is the frequency)
  • Therefore, v = f * λ

Under what conditions are the waves diffracted the most?

Conditions for Maximum Diffraction:

• Waves are diffracted most when they encounter an obstacle with a size similar to their wavelength.
• Smaller wavelengths and larger obstacles result in more pronounced diffraction.

If the length of a simple pendulum is shorten to half then what will be the change in its time period?

Change in Time Period of Simple Pendulum:

• If the length of a simple pendulum is shortened to half, the time period will decrease by approximately 30%.
• This change in time period is inversely proportional to the square root of the length of the pendulum.

Important Long Questions:

Show that vibrating mass spring system performs simple harmonic motion. what is its time period? on what factors it depends?

Vibrating Mass Spring System and Simple Harmonic Motion:

• The system follows simple harmonic motion when the restoring force is proportional to the displacement from the equilibrium position.
• Time Period (T) of the motion depends on the mass (m) and the spring constant (k) according to the formula: T = 2π√(m/k).

What is simple pendulum? Show that vibrating simple pendulum performs simple harmonic motion. What is its time period? on what factors it depends?

Simple Pendulum and Simple Harmonic Motion:

• A simple pendulum consists of a small mass suspended from a fixed point by a string or rod.
• It performs simple harmonic motion when displaced from equilibrium.
• Time Period (T) depends on the length (L) of the pendulum and the acceleration due to gravity (g) according to the formula: T = 2π√(L/g).

What is ripple tank? Describe its construction and working.

Ripple Tank:

A ripple tank is a device used to demonstrate the properties of waves, especially water waves. It consists of a shallow transparent tank filled with water. When waves are generated in the tank, they can be observed directly or projected onto a screen for detailed study. The construction typically includes a light source above the tank, which illuminates the waves, and barriers to create various wave patterns. The working principle involves generating waves using a vibrating paddle or other mechanism and observing their behavior, including reflection, refraction, diffraction, and interference. It's a valuable tool for studying wave phenomena in a controlled environment.

Unit 11: Sound
Important Short Questions: On what factors does the loudness of sound depend?

Factors Affecting Loudness of Sound:

• The loudness of sound depends on the amplitude of the sound waves.
• It also depends on the sensitivity of the ear or the receiver.

What is speed of sound? On what it depends?

Speed of Sound and Factors Affecting It:

• The speed of sound varies depending on the medium through which it travels.
• In general, it travels faster in solids, slower in liquids, and slowest in gases.
• It also depends on temperature, with sound traveling faster in warmer temperatures.

Difference between Loudness and Intensity.

Difference between Loudness and Intensity:

• Loudness is a subjective perception of the strength or volume of a sound as perceived by the ear.
• Intensity is the amount of energy transmitted by sound waves per unit area perpendicular to the direction of wave propagation.

Difference between Noise and Music.

Difference between Noise and Music:

• Noise consists of random, irregular vibrations that produce an unpleasant sound.
• Music consists of organized, periodic vibrations that produce pleasing sounds.

How we are able to distinguish between two sounds having same loudness?

Distinguishing Sounds with the Same Loudness:

• We can distinguish between sounds with the same loudness by their pitch, timbre, and other auditory cues.
• Pitch refers to the frequency of sound waves, while timbre refers to the quality or tone of the sound.

What is pitch of sound? How is it related with the frequency of sound?

Pitch of Sound and Its Relationship with Frequency:

• Pitch is the subjective perception of the frequency of sound waves.
• Higher frequencies are perceived as higher pitches, while lower frequencies are perceived as lower pitches.

How can you prove the mechanical nature of sound by a simple experiment?

Proof of Mechanical Nature of Sound:

• A simple experiment to prove the mechanical nature of sound involves using a tuning fork.
• When a tuning fork is struck and brought close to a resonance chamber filled with water, the sound waves produced cause the water level to oscillate.

Important Long Questions:
Define intensity level. Derive the formula for its decibel scale.

Intensity Level Definition and Derivation of Decibel Scale:

• Intensity Level is a measure of the loudness of sound expressed in decibels (dB).
• Derivation of Decibel Scale Formula:
  • IL (Intensity Level) = 10 * log (I / I₀)
  • Where I is the intensity of the sound wave and I₀ is the reference intensity (threshold of hearing).

What is loudness of sound? On what factors does it depend? Explain with example.

Loudness of Sound and Factors Affecting It:

• Loudness is the subjective perception of the strength or volume of a sound.
• It depends on the intensity of the sound wave, the distance from the source, and the sensitivity of the ear.
• For example, a drum struck with more force will produce a louder sound compared to the same drum struck with less force.

Unit 12: Geometrical Optics

Important Short Questions:
State laws of Reflection.

Laws of Reflection:

• The angle of incidence is equal to the angle of reflection.
• The incident ray, the reflected ray, and the normal to the surface at the point of incidence all lie in the same plane.

State the conditions for total Internal Reflection.

Conditions for Total Internal Reflection:

• Light must travel from a denser medium to a less dense medium.
• The angle of incidence must be greater than the critical angle.

What is Snell’s Law. Write its mathematical form.

Snell’s Law:

• Snell's Law describes the relationship between the angles of incidence and refraction and the refractive indices of two different media.

1. are the angles of incidence and refraction, respectively.goog_294367060

Mathematical form: ${𝑛}_1\sin ({𝜃}_1)={𝑛}_2\sin ({𝜃}_2)$, where ${𝑛}_1$ and ${𝑛}_2$ are the refractive indices of the two media, and ${𝜃}_1$ and
Difference between Nearsightedness ( myopia ) and Farsightedness ( hypermetropia ). How can we remove these defects of vision?

Difference between Nearsightedness (Myopia) and Farsightedness (Hypermetropia):

• Myopia: Distant objects appear blurry because the image forms in front of the retina.
• Hypermetropia: Nearby objects appear blurry because the image forms behind the retina.
• Corrective lenses are used to remedy these vision defects.

Describe how total internal reflection is used in light propagation through optical fibres.

Total Internal Reflection in Optical Fibres:

• Total internal reflection is utilized in optical fibers to transmit light signals over long distances with minimal loss.
• Light entering the fiber at an angle greater than the critical angle undergoes total internal reflection, ensuring the light remains trapped within the fiber.

What is Critical angle? Derive a relationship between the critical angle and refractive index of substance.

Critical Angle and Relationship with Refractive Index:

• The critical angle is the angle of incidence that results in light being refracted along the interface between two media.
• The relationship between the critical angle ($𝑐$) and the refractive index ($𝑛$) is given by: $\sin (𝑐)=\frac{1}{𝑛}$.

Which mirror is used by girls for make up and why?

Makeup Mirror Used by Girls:

• Concave mirrors are preferred for makeup due to their ability to produce an enlarged, virtual, and upright image.
• This allows for better precision while applying makeup.

Difference Real and virtual image.

Difference between Real and Virtual Image:

• Real images are formed by the actual convergence of light rays, and they can be projected onto a screen.
• Virtual images are apparent locations from which light rays appear to diverge, and they cannot be projected onto a screen.

Which mirrors are used for rear view of vehicles and why?

Mirrors Used for Rear View of Vehicles:

• Convex mirrors are employed for the rearview of vehicles because they provide a wider field of view, enabling drivers to see more objects behind them.

What is spherical mirror formula? Write down sigh conventions for spherical mirror formula.

Spherical Mirror Formula and Sign Conventions:

• Spherical Mirror Formula: $\frac{1}{𝑓}=\frac{1}{𝑣}+\frac{1}{𝑢}$
• Sign Conventions:
  • Distances measured in the direction of incident light are taken as positive.
  • Distances measured opposite to the direction of incident light are taken as negative.
  • Heights above the principal axis are taken as positive, and heights below are taken as negative.

Difference between resolving power and magnifying power.

Difference between Resolving Power and Magnifying Power:

• Resolving Power refers to the ability of an optical instrument to distinguish between two closely spaced objects.
• Magnifying Power refers to the degree of enlargement of an image compared to the original object.

Important Long Questions:

Compound Microscope and Telescope

Compound Microscope and Telescope:

• Compound Microscope: Utilizes two lenses (objective and eyepiece) to magnify small objects. The objective lens forms a real inverted image of the object, which is further magnified by the eyepiece.
• Telescope: Uses lenses or mirrors to collect and magnify light from distant objects. The objective lens or primary mirror forms an inverted real image of the object, which is magnified by the eyepiece or secondary mirror for observation.

These responses should comprehensively cover the concepts outlined in Unit 12: Geometrical Optics according to the syllabus.

Unit 13: Electrostatics

Important Short Questions:

State and explain Coulomb’s law.

Coulomb’s Law:

• Coulomb's Law states that the force between two point charges is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them.
• Mathematically, $𝐹=𝑘\frac{{𝑞}_1{𝑞}_2}{{𝑟}^2}$, where $𝐹$ is the electrostatic force, ${𝑞}_1$ and ${𝑞}_2$ are the magnitudes of the charges, $𝑟$ is the distance between them, and $𝑘$ is Coulomb's constant.

Define electric field and electric field intensity.

Electric Field and Electric Field Intensity:

• Electric Field: A region around a charged object where a force would be experienced by another charged object placed in that region.
• Electric Field Intensity: The force experienced per unit positive charge placed at a point in an electric field.

Is electric intensity a vector quantity? what will be its direction?

Electric Intensity as a Vector Quantity:

• Yes, electric intensity is a vector quantity because it has both magnitude and direction.
• Its direction is the direction of the force experienced by a positive test charge placed in the electric field.

What is difference between variable and fixed type capacitor?

Difference between Variable and Fixed Type Capacitor:

• Variable Capacitor: The capacitance of this type of capacitor can be adjusted or varied manually or electronically.
• Fixed Capacitor: The capacitance of this type of capacitor remains constant and cannot be adjusted.

What is capacitance of capacitor? On what factors it depends?

Capacitance of a Capacitor:

• Capacitance is a measure of the ability of a capacitor to store charge per unit voltage.
• It depends on the geometry of the capacitor (such as the area of the plates, the distance between them, and the material between the plates).

Important Long Questions:

Series Combination of Capacitors and Parallel Combination of capacitors.

Series Combination of Capacitors and Parallel Combination of Capacitors:

• Series Combination: Capacitors are connected end-to-end. The total capacitance is less than any individual capacitance, and the total voltage across them is the sum of individual voltages.
• Parallel Combination: Capacitors are connected side by side. The total capacitance is the sum of individual capacitances, and the voltage across each capacitor is the same.

State and explain coulomb’s law. Derive its mathematical form.

Derivation and Explanation of Coulomb’s Law:

• Coulomb's Law describes the electrostatic force between two point charges.
• Derivation involves considering the force experienced by a test charge placed in the electric field produced by another charge.
• The mathematical form is $𝐹=𝑘\frac{{𝑞}_1{𝑞}_2}{{𝑟}^2}$, where $𝐹$ is the force, ${𝑞}_1$ and ${𝑞}_2$ are the magnitudes of the charges, $𝑟$ is the distance between them, and $𝑘$ is Coulomb's constant.

What is Electroscope? Explain its construction and working.

Electroscope: Construction and Working:

• An electroscope is a device used to detect the presence of electric charge.
• Construction: It consists of a metal rod or needle attached to two thin metal leaves suspended from a metal rod.
• Working: When a charged object is brought near the metal rod, the like charges repel each other, causing the metal leaves to diverge. This divergence indicates the presence of electric charge.

Unit 14: Current Electricity

Important Short Questions:

Difference between Electronic current and conventional current?

Difference between Electronic Current and Conventional Current:

• Electronic current refers to the flow of electrons in a circuit, moving from the negative terminal of a battery to the positive terminal.
• Conventional current refers to the flow of positive charges in a circuit, from the positive terminal of a battery to the negative terminal.

Describe Ohm’s law and its limitations.

Ohm’s Law and Its Limitations:

• Ohm's Law states that the current flowing through a conductor is directly proportional to the potential difference across it, provided the temperature remains constant.
• Limitations: Ohm's Law is not applicable to all conductors, especially non-ohmic conductors like diodes and semiconductors.

Distinguish between D.C and A.C

Distinguishing Between D.C and A.C:

• Direct Current (D.C) flows in one direction only, typically provided by batteries or DC power supplies.
• Alternating Current (A.C) changes direction periodically, typically provided by power grids and generators.

Can current flow through a circuit without potential difference ? Explain.

Current Flow Without Potential Difference:

• No, current cannot flow through a circuit without a potential difference.
• Potential difference provides the driving force for the flow of charges in a circuit.

What is meant by term e.m.f? Is it really a force? Explain.

Meaning of e.m.f and Its Nature:

• Electromotive Force (e.m.f) is the potential difference across the terminals of a source when no current is flowing.
• It's not a force in the mechanical sense but rather a measure of the energy provided to each unit of charge by the source.

Difference between the following. i. emf and potential difference ii. ohmic and non ohmic conductor
Difference Between:

• i. e.m.f and Potential Difference: e.m.f is the total energy per unit charge provided by the source, while potential difference is the energy per unit charge used up by the components in the circuit.
• ii. Ohmic and Non-Ohmic Conductor: Ohmic conductors obey Ohm's Law, while non-ohmic conductors do not follow Ohm's Law and exhibit varying resistance with changes in voltage or current.

State and prove joule’s law of heating.

Joule’s Law of Heating:

• Joule's Law states that the heat produced in a conductor is directly proportional to the square of the current passing through it, the resistance of the conductor, and the time for which the current flows.
• Mathematically, $𝐻={𝐼}^2𝑅𝑡$, where $𝐻$ is the heat produced, $𝐼$ is the current, $𝑅$ is the resistance, and $𝑡$ is the time.

What is resistance? On what factors does it depend?

Resistance and Its Factors:

• Resistance is the opposition offered by a conductor to the flow of current.
• It depends on the length, cross-sectional area, material, and temperature of the conductor.

Show that 1kWh = 3.6MJ or show that volt ampere is equal to watt.

Conversion: 1 kWh = 3.6 MJ or Volt-Ampere to Watt:

• 1 kWh (kilowatt-hour) is equal to 3.6 MJ (megajoules), where 1 kWh is the energy consumed by a 1 kW device operating for 1 hour.
• 1 Volt-Ampere (VA) is equal to 1 Watt (W), as they both measure power in electrical circuits.

Important Long Questions:

Series Combination of Resistors and Parallel Combination of Resistors.

Series Combination of Resistors and Parallel Combination of Resistors:

• Series Combination: Resistors are connected end-to-end, and the total resistance is the sum of individual resistances.
• Parallel Combination: Resistors are connected side by side, and the reciprocal of the total resistance is the sum of the reciprocals of individual resistances.

Unit 15: Electromagnetism

Important Short Questions:

Explain that an electric current in a conductor produces a magnetic field around it.

Magnetic Field Produced by Electric Current:

• An electric current in a conductor produces a magnetic field around it according to Ampere's circuital law.
• The direction of the magnetic field can be determined using the right-hand rule, where the thumb points in the direction of current flow, and the fingers curl in the direction of the magnetic field lines.

List factors affecting the magnitude of an induced e.m.f.

Factors Affecting the Magnitude of an Induced e.m.f:

• The rate of change of magnetic flux.
• The number of turns in the coil.
• The strength of the magnetic field.
• The angle between the magnetic field and the coil.

Right hand rule , Fleming’s left hand rule and Lenz’s Law

Right-Hand Rule, Fleming’s Left-Hand Rule, and Lenz’s Law:

• Right-Hand Rule: Used to determine the direction of the magnetic field produced by a current-carrying conductor.
• Fleming’s Left-Hand Rule: Used to determine the direction of the force experienced by a current-carrying conductor placed in a magnetic field.
• Lenz’s Law: States that the direction of an induced current is such that it opposes the change in magnetic flux that produced it.

Difference between generator and motor.

Difference Between Generator and Motor:

• Generator: Converts mechanical energy into electrical energy by electromagnetic induction.
• Motor: Converts electrical energy into mechanical energy by the interaction between magnetic fields and current-carrying conductors.

In what way split rings in DC motor differ from slip rings in AC motor in working?

Split Rings in DC Motor vs. Slip Rings in AC Motor:

• In a DC motor, split rings (also known as commutators) are used to reverse the direction of the current in the coil every half rotation, ensuring continuous rotation in the same direction.
• In an AC motor, slip rings are used to transfer electrical power to the rotating part (rotor) without reversing the direction of the current.

Important Long Questions:

DC motor, AC Generator and Transformer ( Define, Construction and working )

1. DC Motor:

   • Definition: A DC motor is a device that converts electrical energy into mechanical energy through the interaction of magnetic fields and current-carrying conductors.
   • Construction: It consists of a coil (armature) placed in a magnetic field between the poles of a permanent magnet or an electromagnet. Brushes and split rings (commutator) are used to provide electrical connection to the coil.
   • Working: When a current is passed through the coil, it experiences a force due to the interaction between the magnetic field and the current, causing it to rotate.

2. AC Generator:

   • Definition: An AC generator (alternator) is a device that converts mechanical energy into electrical energy through electromagnetic induction.
   • Construction: It consists of a coil (armature) rotating between the poles of a magnet (permanent magnet or electromagnet). Slip rings are used to collect the induced current.
   • Working: When the coil rotates, it cuts across magnetic field lines, inducing an e.m.f according to Faraday's law of electromagnetic induction.

3. Transformer:

• Definition: A transformer is a device used to step up or step down alternating voltage levels while maintaining the frequency.
• Construction: It consists of two coils (primary and secondary) wound around a laminated iron core. The coils are electrically isolated but magnetically coupled.

• Working: When an alternating current flows through the primary coil, it produces a changing magnetic field, inducing a voltage in the secondary coil through mutual induction.

Unit 16: Introductory Electronics

Important Short Questions

Difference between Analogue and digital electronics

Difference between Analogue and Digital Electronics:

• Analog Electronics: Deals with continuous signals that vary smoothly over time, such as voltage or current. Analog devices can represent an infinite number of states.
• Digital Electronics: Deals with discrete signals that have only two possible states, typically represented as 0 or 1. Digital devices process information in a binary format.

Explain the process of Thermionic Emission emitted from a filament. Name two factors which can enhance thermionic emission.

Thermionic Emission Process:

• Thermionic emission is the process by which electrons are emitted from the surface of a heated filament.
• Electrons gain enough thermal energy to overcome the work function of the material and escape into the surrounding space.
• Factors enhancing thermionic emission: Increasing the temperature of the filament and reducing the work function of the material.

How can you that cathode rays are negatively charge? Give three reasons.

Evidence of Negative Charge in Cathode Rays:

• Deflection by electric field: Cathode rays are deflected towards the positively charged plate, indicating that they carry a negative charge.
• Deflection by magnetic field: Cathode rays are deflected in the opposite direction to positively charged particles, indicating that they are negatively charged.
• Production of X-rays when striking a target: When cathode rays strike a target, X-rays are produced, suggesting that they are negatively charged particles.

How can you control brightness of waveform on screen of CRO?

• Controlling Brightness of Waveform on CRO Screen:

• The brightness of the waveform on the screen of a Cathode Ray Oscilloscope (CRO) can be controlled by adjusting the intensity control knob or by varying the voltage applied to the electron gun.

Is NAND gate reciprocal of AND gate?

Reciprocity of NAND Gate and AND Gate:

• No, NAND gate is not the reciprocal of AND gate. Reciprocity implies that the function of one gate can be obtained by interchanging the inputs and outputs of another gate. NAND gate is not the reciprocal of AND gate because they have different logic functions.

Describe the effect of electric and magnetic field on electron beam?

Effect of Electric and Magnetic Fields on Electron Beam:

• Electric Field: Affects the speed and direction of the electron beam. A positive electric field accelerates the beam, while a negative electric field decelerates it.
• Magnetic Field: Affects the path of the electron beam. A perpendicular magnetic field causes the beam to bend, with the direction of bending determined by the right-hand rule.

Important Long Questions
Logic Gates ( AND , OR , NOT , NAND and NOR )

Logic Gates (AND, OR, NOT, NAND, and NOR):

• AND Gate: Outputs 1 only if all inputs are 1.
• OR Gate: Outputs 1 if any input is 1.
• NOT Gate: Inverts the input.
• NAND Gate: Outputs 0 if all inputs are 1.
• NOR Gate: Outputs 1 only if all inputs are 0.
• Describe their truth tables and logic symbol representations.

What is Electron Gun? Describe its construction and working.

Electron Gun:

• Construction: Consists of a heated cathode filament, a control grid, and an anode plate. Electrons are emitted from the heated filament, controlled by the grid, and accelerated towards the anode.
• Working: When the filament is heated, thermionic emission occurs, releasing electrons. The grid controls the flow of electrons, allowing for modulation, while the anode accelerates the electrons towards the screen.

What is Cathode Ray Oscilloscope? Describe the working of its different parts and uses.

Cathode Ray Oscilloscope (CRO):

• Description: An electronic test instrument used to display and analyze the waveform of electrical signals.
• Working of Different Parts: Includes the electron gun, deflection plates, and screen. The electron beam from the gun is deflected by the plates according to the input signal, resulting in a visual representation on the screen.
• Uses: Used in various applications such as testing and troubleshooting electronic circuits, measuring voltage, frequency, and waveform characteristics.

Unit 17: Information and Communication Technology

Important Short Questions:

Difference between the following. i. Data and Information ii. RAM and ROM iii. Hardware and Software

1. Difference between Data and Information:

   • Data: Raw facts and figures that have no meaning by themselves.
   • Information: Processed and organized data that provides context, relevance, and meaning.

2. Difference between RAM and ROM:

   • RAM (Random Access Memory): Volatile memory used for temporary storage of data and program instructions. It is fast but loses its contents when power is turned off.
   • ROM (Read-Only Memory): Non-volatile memory used for permanent storage of data and program instructions. It retains its contents even when power is turned off and is typically used to store firmware or system software.

3. Difference between Hardware and Software:

   • Hardware: Physical components of a computer system that can be touched and seen, such as the CPU, memory, keyboard, and monitor.
   • Software: Programs and instructions that tell the hardware what to do, including operating systems, applications, and utilities.

Why optical fibre is better than electric wire for communication process.

Advantages of Optical Fiber over Electric Wire for Communication:

• Greater bandwidth: Optical fibers can carry much more data over longer distances compared to electric wires.
• Immunity to electromagnetic interference: Optical fibers are not affected by electromagnetic interference, ensuring clearer communication.
• Lower attenuation: Optical fibers experience less signal loss over distance compared to electric wires.
• Lightweight and compact: Optical fibers are smaller and lighter than traditional electric wires, making installation easier and less intrusive.

Explain briefly the transmission of radiowaves through air.

Transmission of Radiowaves through Air:

• Radio waves are electromagnetic waves with frequencies ranging from a few kilohertz to hundreds of gigahertz.
• They are transmitted through the atmosphere in a straight line and are affected by factors such as distance, frequency, and obstacles in the path.
• Radiowaves can be transmitted using antennas, which convert electrical signals into electromagnetic waves and vice versa.

How are light signals sent through optical fibre?

Transmission of Light Signals through Optical Fiber:

• Light signals are sent through optical fibers using the principle of total internal reflection.
• The core of the optical fiber, made of glass or plastic, has a higher refractive index than the cladding surrounding it.
• When light enters the core at a shallow angle, it undergoes total internal reflection and is confined within the core, allowing it to travel long distances without significant loss.

Unit 18: Radioactivity

Important Short Questions

What is meant by background radiations? List some sources of background radiations.

Background Radiations:

• Background radiations refer to the ionizing radiation that exists in the environment from various natural and artificial sources.
• Sources of background radiations include cosmic rays from space, radioactive elements in soil and rocks, radon gas, medical procedures, and nuclear fallout.

Explain alpha, beta, and gamma decay.

Alpha, Beta, and Gamma Decay:

• Alpha Decay: Involves the emission of an alpha particle (two protons and two neutrons) from the nucleus.
• Beta Decay: Involves the emission of a beta particle (an electron or positron) from the nucleus.
• Gamma Decay: Involves the emission of gamma rays, which are electromagnetic radiation, from the nucleus to stabilize it after alpha or beta decay.

Explain the process of Carbon Dating.

Carbon Dating Process:

• Carbon dating is a method used to determine the age of organic materials based on the decay of radioactive carbon-14 (^14C) isotopes.
• Organisms absorb carbon-14 from the atmosphere during their lifetime, and the ratio of carbon-14 to stable carbon-12 (^12C) decreases over time due to radioactive decay. By measuring this ratio, the age of the sample can be calculated.

What is Half-Life? Derive the formula for the number of undecayed atoms. Draw a graph for decaying atoms with time.

Half-Life:

• Half-life is the time taken for half of the radioactive nuclei in a sample to decay.
• The formula for the number of undecayed atoms after $𝑛$ half-lives is given by: $𝑁={𝑁}_0{\left(\frac{1}{2}\right)}^{𝑛}$, where ${𝑁}_0$ is the initial number of atoms.
• The graph of decaying atoms with time is exponential decay, where the number of undecayed atoms decreases exponentially with time.

What fraction of a radioactive element will be left after 4 half-lives have elapsed?

Fraction of Radioactive Element After 4 Half-Lives:

• After 4 half-lives, ${\left(\frac{1}{2}\right)}^4=\frac{1}{16}$ of the radioactive element will be left.

How long will it take for a radioactive element to decay completely?

Time Taken for Radioactive Element to Decay Completely:

• A radioactive element never completely decays; however, it can decay to a negligible amount over a period of many half-lives.

Why do nuclei of atoms with atomic numbers greater than 82 emit radiations?

Emission of Radiations by Nuclei with Atomic Numbers Greater Than 82:

• Nuclei with atomic numbers greater than 82 are unstable and undergo radioactive decay to achieve stability by emitting alpha, beta, or gamma radiations.

Is radioactivity a spontaneous process? Elaborate on your answer with a simple experiment.

Is Radioactivity a Spontaneous Process?

• Yes, radioactivity is a spontaneous process because it occurs without external influence or stimulation.
• An example of a simple experiment demonstrating this spontaneity is the observation of the spontaneous decay of a radioactive sample over time, without any external triggering factors.

Important Long Questions

Fission Reaction and Nuclear Fusion.

Fission Reaction and Nuclear Fusion:

• Fission Reaction: Involves the splitting of heavy atomic nuclei into smaller nuclei, releasing a large amount of energy. This process is used in nuclear power plants and atomic bombs.

• Nuclear Fusion: Involves the merging of light atomic nuclei to form a heavier nucleus, releasing a tremendous amount of energy. This process powers the sun and stars and is being researched for energy production on Earth.

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Physics, Class 10, Federal Board, Syllabus, Short Questions, Long Questions, Simple Harmonic Motion, Waves, Sound, Geometrical Optics, Electrostatics, Current Electricity, Electromagnetism, Introductory Electronics, Information and Communication Technology, Radioactivity