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JCE Physics practice questions

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Question 1Physics

A body moves along a straight line with constant acceleration. Which quantity is represented by the area under its velocity–time graph?

  1. The acceleration of the body
  2. The total force acting on the body
  3. The displacement of the body Correct answer.
  4. The rate of change of acceleration

Explanation

The area under a velocity–time graph equals the integral of velocity with respect to time, which is displacement. The gradient of the same graph gives acceleration, not the area. Force would require mass, which the graph does not contain.

Question 2Physics

A stone is dropped from rest and falls freely near the Earth's surface, where air resistance is negligible. After 3.0 s, what is its speed? Take g = 9.8 m/s².

  1. 44.1 m/s
  2. 29.4 m/s Correct answer.
  3. 88.2 m/s
  4. 9.8 m/s

Explanation

For free fall from rest, v = gt, so v = 9.8 × 3.0 = 29.4 m/s. The value 44.1 m/s arises from using ½gt² (a distance, not a speed). Doubling to 88.2 m/s would require 6 s of fall.

Question 3Physics

A resultant force acts on a body of fixed mass. According to Newton's second law, the acceleration of the body is directly proportional to which quantity?

  1. The body's momentum
  2. The resultant force Correct answer.
  3. The body's kinetic energy
  4. The body's displacement

Explanation

Newton's second law states F = ma, so for constant mass the acceleration is proportional to the resultant force and in the same direction. Momentum and kinetic energy depend on velocity and are not the proportionality basis here. Displacement does not determine acceleration.

Question 4Physics

Two forces of 6 N and 8 N act at a single point at right angles to each other. What is the magnitude of their resultant?

  1. 7 N
  2. 10 N Correct answer.
  3. 14 N
  4. 2 N

Explanation

Perpendicular vectors add by Pythagoras: R = √(6² + 8²) = √100 = 10 N. Simple addition (14 N) only applies when the forces are parallel and in the same direction. The difference (2 N) applies when they are antiparallel.

Question 5Physics

A car travels a circular track of radius 50 m at a constant speed of 20 m/s. What is the magnitude of its centripetal acceleration?

  1. 400 m/s²
  2. 4.0 m/s²
  3. 8.0 m/s² Correct answer.
  4. 0.4 m/s²

Explanation

Centripetal acceleration is a = v²/r = 20²/50 = 400/50 = 8.0 m/s². It points toward the centre of the circle even though the speed is constant. Using v/r instead of v²/r gives the incorrect 0.4 m/s².

Question 6Physics

Which statement correctly describes the work done by a force on a body?

  1. Work equals force divided by the time of contact
  2. Work equals the mass multiplied by the acceleration
  3. Work equals force multiplied by the displacement component along the force Correct answer.
  4. Work equals the force multiplied by the total time

Explanation

Work is the scalar product of force and displacement, W = Fd cos θ, so only the displacement component along the force contributes. Multiplying force by time gives impulse, not work. Mass times acceleration is force itself.

Question 7Physics

A spring obeys Hooke's law with spring constant 200 N/m. What extension is produced by a stretching force of 10 N?

  1. 2.0 m
  2. 0.05 m Correct answer.
  3. 2000 m
  4. 0.20 m

Explanation

Hooke's law gives F = kx, so x = F/k = 10/200 = 0.05 m. The extension is proportional to the applied force within the elastic limit. Multiplying instead of dividing gives the incorrect 2000 m.

Question 8Physics

In a transverse wave travelling along a stretched string, what is the direction of particle oscillation relative to the direction of energy transfer?

  1. Perpendicular to the direction of energy transfer Correct answer.
  2. Parallel to the direction of energy transfer
  3. Random and independent of the direction of energy transfer
  4. At 45° to the direction of energy transfer

Explanation

By definition, in a transverse wave the particles oscillate perpendicular to the direction in which the wave (and its energy) travels. A longitudinal wave has oscillations parallel to the propagation direction. The 45° and random descriptions match no standard wave type.

Question 9Physics

A ray of light passes from air into glass of refractive index 1.5 at an angle of incidence of 30°. What is the angle of refraction? Take sin 30° = 0.50.

  1. About 19.5° Correct answer.
  2. About 45°
  3. About 60°
  4. About 30°

Explanation

Snell's law gives n₁ sin θ₁ = n₂ sin θ₂, so sin θ₂ = (1.0 × 0.50)/1.5 = 0.333, giving θ₂ ≈ 19.5°. The ray bends toward the normal because glass is optically denser than air. An unchanged angle would only occur if the refractive indices were equal.

Question 10Physics

A resistor of 12 Ω carries a current of 0.50 A. What is the power dissipated in the resistor?

  1. 12 W
  2. 24 W
  3. 3.0 W Correct answer.
  4. 6.0 W

Explanation

Power can be found from P = I²R = (0.50)² × 12 = 0.25 × 12 = 3.0 W. Equivalently, the voltage is IR = 6.0 V, and P = VI = 3.0 W. Substituting the current without squaring gives the incorrect 6.0 W.

Question 11Physics

Two point charges are separated by a fixed distance in a vacuum. If the distance between them is doubled, how does the magnitude of the electrostatic force change?

  1. It becomes twice as large
  2. It stays the same
  3. It becomes four times larger
  4. It becomes one quarter as large Correct answer.

Explanation

Coulomb's law states F ∝ 1/r², so doubling the separation reduces the force to one quarter of its original value. The inverse-square dependence means the force does not simply halve. Charge magnitudes are unchanged here.

Question 12Physics

A 2.0 kg trolley moving at 3.0 m/s collides with and sticks to a stationary 4.0 kg trolley on a frictionless track. What is their common velocity after the collision?

  1. 0.50 m/s
  2. 1.5 m/s
  3. 1.0 m/s Correct answer.
  4. 2.0 m/s

Explanation

Momentum is conserved: (2.0 × 3.0) = (2.0 + 4.0) × v, so 6.0 = 6.0v and v = 1.0 m/s. The collision is perfectly inelastic, so kinetic energy is not conserved. Using only the moving mass in the denominator gives the incorrect 3.0 m/s scenario.

Question 13Physics

An ideal gas is compressed at constant temperature. According to the kinetic theory of gases, what happens to the average kinetic energy of its molecules?

  1. It becomes zero because the gas is compressed
  2. It decreases because the volume is smaller
  3. It increases because the molecules are closer together
  4. It remains unchanged because the temperature is constant Correct answer.

Explanation

For an ideal gas the average translational kinetic energy of molecules depends only on absolute temperature, E = (3/2)kT. At constant temperature it stays the same even though the volume changes. Compression at constant temperature raises pressure instead.

Question 14Physics

A gas absorbs 500 J of heat and does 200 J of work on its surroundings. What is the change in its internal energy?

  1. 700 J
  2. −300 J
  3. 300 J Correct answer.
  4. −700 J

Explanation

The first law gives ΔU = Q − W, where Q is heat added to the gas and W is work done by the gas. Here ΔU = 500 − 200 = +300 J. Adding the two quantities instead gives the incorrect 700 J.

Question 15Physics

A simple pendulum has a period of 2.0 s on Earth. What happens to its period if it is taken to a place where the gravitational field strength is four times larger?

  1. It doubles to 4.0 s
  2. It becomes 0.50 s
  3. It stays at 2.0 s
  4. It halves to 1.0 s Correct answer.

Explanation

The period of a simple pendulum is T = 2π√(l/g), so T ∝ 1/√g. Quadrupling g reduces T by a factor of √4 = 2, giving 1.0 s. The period is independent of the mass of the bob.

Question 16Physics

A sound wave of frequency 500 Hz travels through air at 340 m/s. What is its wavelength?

  1. 1.7 m
  2. 0.17 m
  3. 0.34 m
  4. 0.68 m Correct answer.

Explanation

The wave equation gives λ = v/f = 340/500 = 0.68 m. Wavelength is inversely proportional to frequency for a fixed wave speed. Multiplying frequency by speed instead of dividing gives a value far too large.

Question 17Physics

A potential difference of 12 V is applied across two resistors of 4 Ω and 6 Ω connected in series. What is the current in the circuit?

  1. 2.0 A
  2. 1.2 A Correct answer.
  3. 0.83 A
  4. 5.0 A

Explanation

In series the resistances add: R = 4 + 6 = 10 Ω, so I = V/R = 12/10 = 1.2 A. The same current flows through both resistors. Using only one resistance or ignoring the total gives the other values.

Question 18Physics

A transformer has 400 turns on its primary coil and 100 turns on its secondary. If the primary is supplied with 240 V alternating current, what is the secondary voltage (assume ideal)?

  1. 30 V
  2. 60 V Correct answer.
  3. 960 V
  4. 120 V

Explanation

For an ideal transformer, V₂/V₁ = N₂/N₁, so V₂ = 240 × (100/400) = 60 V. This is a step-down transformer because the secondary has fewer turns. Reversing the ratio gives the incorrect 960 V.

Question 19Physics

A photon of light has a frequency of 6.0 × 10¹⁴ Hz. Using Planck's constant h = 6.6 × 10⁻³⁴ J·s, what is the photon energy?

  1. About 1.1 × 10⁻⁴⁸ J
  2. About 3.6 × 10⁻¹⁹ J
  3. About 4.0 × 10⁻¹⁹ J Correct answer.
  4. About 9.1 × 10⁻²⁰ J

Explanation

Photon energy is E = hf = 6.6 × 10⁻³⁴ × 6.0 × 10¹⁴ ≈ 4.0 × 10⁻¹⁹ J. This corresponds to visible light. Dividing instead of multiplying gives an absurdly small value.

Question 20Physics

In a nuclear fission reaction, a heavy nucleus splits into two lighter nuclei and several neutrons. Why is energy released in this process?

  1. The products have a larger total rest mass than the original nucleus
  2. The total charge of the products is greater than that of the original nucleus
  3. The total mass of the products is slightly less than the mass of the original nucleus Correct answer.
  4. The neutrons carry away all the binding energy as kinetic energy

Explanation

The products have slightly less total rest mass than the original nucleus, and the missing mass appears as energy according to E = mc². This mass difference reflects the greater binding energy per nucleon of the products. Charge is conserved in fission, not increased.

Question 21Physics

A body moves in a straight line under a constant resultant force. Which pair of quantities both change at a constant rate during the motion?

  1. Velocity and displacement
  2. Kinetic energy and displacement
  3. Displacement and momentum
  4. Momentum and kinetic energy Correct answer.

Explanation

Constant force means constant acceleration, so velocity and momentum change linearly with time at constant rates. Kinetic energy depends on the square of velocity, so it also changes at a constant rate under constant acceleration. Displacement changes quadratically, so its rate is not constant.

Question 22Physics

A block slides down a rough incline at constant speed. Which statement correctly describes the energy transfers involved?

  1. Kinetic energy increases while gravitational potential energy stays constant
  2. Gravitational potential energy decreases and is converted to internal energy by friction, with kinetic energy constant Correct answer.
  3. Gravitational potential energy decreases and is entirely converted to kinetic energy
  4. Both gravitational potential energy and kinetic energy increase during the slide

Explanation

Constant speed means kinetic energy does not change, so the loss of gravitational potential energy is balanced by work done against friction, which raises the internal energy of the block and incline. If the incline were smooth, the potential energy would become kinetic energy instead.

Question 23Physics

A gas undergoes an adiabatic expansion. Which statement about the process is correct?

  1. The internal energy of the gas increases as it expands
  2. No heat enters or leaves the gas, so its internal energy falls as it does work Correct answer.
  3. Heat flows into the gas to keep its temperature constant
  4. The gas does no work because no heat is supplied

Explanation

Adiabatic means Q = 0, so the first law gives ΔU = −W. When the gas expands and does positive work, its internal energy decreases and its temperature falls. An isothermal process, by contrast, requires heat input to hold temperature constant.

Question 24Physics

A charged particle enters a uniform magnetic field with its velocity perpendicular to the field lines. Which statement describes its subsequent motion?

  1. It accelerates along the field lines because the force is parallel to the field
  2. It spirals outward with increasing speed because the magnetic force adds kinetic energy
  3. It moves in a straight line at constant speed because the magnetic force does no work
  4. It moves in a circular path at constant speed because the magnetic force acts perpendicular to its velocity Correct answer.

Explanation

The magnetic force F = qvB is always perpendicular to the velocity, so it changes direction but not speed, producing uniform circular motion. Because the force is perpendicular to displacement, it does no work and kinetic energy stays constant. A velocity component along the field would instead give a helical path.

Question 25Physics

In a photoelectric experiment, light of a given frequency above the threshold is shone on a metal surface, and the intensity is doubled while the frequency is kept constant. What happens to the maximum kinetic energy of the emitted electrons and to the number emitted per second?

  1. The maximum kinetic energy doubles and the emission rate is unchanged
  2. Both the maximum kinetic energy and the emission rate are unchanged
  3. The maximum kinetic energy is unchanged and the emission rate doubles Correct answer.
  4. Both the maximum kinetic energy and the emission rate double

Explanation

Maximum kinetic energy depends only on the photon frequency through hf = φ + K_max, so it is unaffected by intensity. Doubling the intensity doubles the number of photons arriving per second, so twice as many electrons are emitted per second. The work function of the metal is unchanged.

Question 26Physics

A cyclist travels 120 m due east in 20 s and then 80 m due west in 20 s. What is the magnitude of the cyclist's average velocity for the whole journey?

  1. 1.0 m/s Correct answer.
  2. 10 m/s
  3. 2.0 m/s
  4. 5.0 m/s

Explanation

Average velocity uses total displacement divided by total time. The displacement is 120 m east minus 80 m west, giving 40 m east, so the magnitude is 40 m / 40 s = 1.0 m/s. Average speed would instead use the total distance of 200 m, giving 5.0 m/s.

Question 27Physics

A stone is dropped from rest from a cliff and falls freely. Taking g = 9.8 m/s² and ignoring air resistance, how far does it fall in the first 3.0 s?

  1. 88.2 m
  2. 44.1 m Correct answer.
  3. 14.7 m
  4. 29.4 m

Explanation

For motion from rest under constant acceleration, the displacement is s = ½gt². Substituting gives ½ × 9.8 × (3.0)² = 44.1 m. The velocity after 3.0 s would be 29.4 m/s, which is a velocity, not a distance.

Question 28Physics

A force of 30 N acts on a body of mass 6.0 kg that is free to move on a frictionless horizontal surface. What is the acceleration of the body?

  1. 36 m/s²
  2. 0.20 m/s²
  3. 180 m/s²
  4. 5.0 m/s² Correct answer.

Explanation

Newton's second law states that the resultant force equals mass times acceleration, so a = F/m. Dividing 30 N by 6.0 kg gives 5.0 m/s². The direction of the acceleration is the same as the direction of the resultant force.

Question 29Physics

A uniform metre rule is pivoted at its centre and balanced. A 2.0 N weight hangs 30 cm from the pivot on the left side. How far from the pivot must a 3.0 N weight hang on the right side to keep the rule balanced?

  1. 20 cm Correct answer.
  2. 10 cm
  3. 45 cm
  4. 15 cm

Explanation

For rotational equilibrium about the pivot, the clockwise moment must equal the anticlockwise moment. The left moment is 2.0 N × 30 cm = 60 N·cm, so the right distance is 60 N·cm ÷ 3.0 N = 20 cm. The larger force needs the shorter lever arm to produce the same moment.

Question 30Physics

A wave has a frequency of 25 Hz and a wavelength of 4.0 m. What is its speed?

  1. 100 m/s Correct answer.
  2. 29 m/s
  3. 0.16 m/s
  4. 6.3 m/s

Explanation

The wave equation relates speed, frequency and wavelength as v = fλ. Multiplying 25 Hz by 4.0 m gives 100 m/s. Frequency is the number of oscillations per second and wavelength is the distance between successive corresponding points.

Question 31Physics

Which statement correctly describes the electric field between two large parallel plates carrying equal and opposite charges?

  1. It is strongest at the centre and weaker near the plates.
  2. It is uniform and directed from the negative plate to the positive plate.
  3. It is zero everywhere between the plates because the charges cancel.
  4. It is uniform and directed from the positive plate to the negative plate. Correct answer.

Explanation

Between oppositely charged parallel plates the fields from each plate reinforce to give a uniform field, except near the edges. Field lines point in the direction of the force on a positive test charge, which is from the positive plate towards the negative plate.

Question 32Physics

A current-carrying wire lies at right angles to a uniform magnetic field. Which change would double the magnitude of the magnetic force on the wire?

  1. Rotating the wire so it lies parallel to the field
  2. Reversing the direction of the current
  3. Halving the current while keeping the length constant
  4. Doubling the length of wire in the field while keeping the current constant Correct answer.

Explanation

The force on a straight wire is F = BIL sin θ, so the force is proportional to the length of wire within the field. Doubling the length while keeping current and field constant doubles the force. Reversing the current reverses the direction of the force but not its magnitude.

Question 33Physics

Which statement correctly describes the energy changes in a filament lamp connected to a battery?

  1. The battery supplies only light energy directly to the lamp.
  2. Chemical energy in the battery is converted to electrical energy, which is then transferred to thermal and light energy in the lamp. Correct answer.
  3. Electrical energy is created in the lamp and stored there permanently.
  4. Thermal energy from the surroundings is converted into electrical energy in the lamp.

Explanation

A battery converts stored chemical energy into electrical energy, which is carried by the current. In the filament lamp, resistance converts this electrical energy mainly into thermal energy and some light. Energy is conserved throughout, only its form changes.

Question 34Physics

A car of mass 800 kg accelerates uniformly from rest to 20 m/s in 8.0 s. What is the average resultant force on the car?

  1. 160 N
  2. 16000 N
  3. 2000 N Correct answer.
  4. 3200 N

Explanation

The acceleration is the change in velocity divided by time, giving 20 m/s ÷ 8.0 s = 2.5 m/s². Applying F = ma gives 800 kg × 2.5 m/s² = 2000 N. This is the resultant force, so resistive forces must be accounted for if the engine force is required.

Question 35Physics

A projectile is launched horizontally from a cliff top with a speed of 15 m/s. Taking g = 9.8 m/s² and ignoring air resistance, what is its vertical velocity after 2.0 s?

  1. 9.8 m/s downwards
  2. 4.9 m/s downwards
  3. 30 m/s downwards
  4. 19.6 m/s downwards Correct answer.

Explanation

Horizontal and vertical motions are independent. The initial vertical velocity is zero, so the vertical velocity after time t is gt = 9.8 × 2.0 = 19.6 m/s downwards. The horizontal speed of 15 m/s remains constant throughout the flight.

Question 36Physics

A block of mass 5.0 kg is pulled along a rough horizontal floor by a horizontal force of 40 N. A constant friction force of 15 N acts on the block. What is the acceleration of the block?

  1. 3.0 m/s²
  2. 8.0 m/s²
  3. 11 m/s²
  4. 5.0 m/s² Correct answer.

Explanation

The resultant horizontal force is the applied force minus friction, giving 40 N − 15 N = 25 N. Newton's second law then gives a = 25 N ÷ 5.0 kg = 5.0 m/s². Using the applied force alone would overstate the acceleration.

Question 37Physics

A ball of mass 0.20 kg hits a wall horizontally at 6.0 m/s and rebounds horizontally at 4.0 m/s. The contact time is 0.050 s. What is the magnitude of the average force exerted by the wall on the ball?

  1. 24 N
  2. 8.0 N
  3. 200 N
  4. 40 N Correct answer.

Explanation

Taking the initial direction as positive, the change in momentum is m(v − u) = 0.20 × (−4.0 − 6.0) = −2.0 kg·m/s. The magnitude of the average force is the magnitude of this change divided by time: 2.0 ÷ 0.050 = 40 N. The rebound means the velocity change is 10 m/s in magnitude, not 2 m/s.

Question 38Physics

A solid sphere and a hollow spherical shell have the same mass and the same external radius. Both roll without slipping down the same incline from rest. Which object reaches the bottom first?

  1. The solid sphere, because more of its mass is closer to the axis, giving a smaller moment of inertia. Correct answer.
  2. The hollow shell, because its mass is concentrated at the rim, giving it greater rotational inertia.
  3. They arrive together, because rolling friction is the same for both.
  4. They arrive together, because their masses and radii are equal.

Explanation

For the same mass and radius, a solid sphere has a smaller moment of inertia than a hollow shell. A smaller fraction of the gravitational potential energy goes into rotation, leaving more for translational motion, so the solid sphere accelerates more and arrives first.

Question 39Physics

A hydraulic press has a small piston of area 5.0 cm² and a large piston of area 200 cm². A force of 60 N is applied to the small piston. What force is produced on the large piston, assuming the system is ideal?

  1. 1.5 N
  2. 240 N
  3. 2400 N Correct answer.
  4. 6000 N

Explanation

By Pascal's principle, pressure is transmitted equally, so F₁/A₁ = F₂/A₂. The area ratio is 200 ÷ 5.0 = 40, so the output force is 60 N × 40 = 2400 N. The press multiplies force at the expense of the distance moved by the large piston.

Question 40Physics

A liquid of density 1000 kg/m³ stands in a vertical tube to a height of 4.0 m. Taking g = 10 m/s², what is the pressure at the base due to the liquid alone?

  1. 400000 Pa
  2. 250 Pa
  3. 40000 Pa Correct answer.
  4. 4000 Pa

Explanation

Hydrostatic pressure due to a liquid column is p = ρgh. Substituting 1000 × 10 × 4.0 gives 40000 Pa. The pressure depends on depth and density, not on the cross-sectional area of the tube.

Question 41Physics

A sealed container holds an ideal gas at constant volume. The temperature of the gas is increased from 300 K to 600 K. What happens to the pressure of the gas?

  1. It doubles. Correct answer.
  2. It halves.
  3. It increases by a factor of four.
  4. It stays the same.

Explanation

At constant volume, pressure is directly proportional to absolute temperature, as stated by p/T = constant. Doubling the absolute temperature from 300 K to 600 K therefore doubles the pressure. Temperatures must be in kelvin, and 300 K to 600 K is indeed a doubling.

Question 42Physics

A gas is taken through a complete cycle and returns to its initial state. Which statement about the net work done by the gas over the cycle is correct?

  1. It is always zero because the gas returns to its initial state.
  2. It equals the change in internal energy over the cycle.
  3. It is always negative because work is done on the gas.
  4. It equals the net heat absorbed by the gas over the cycle. Correct answer.

Explanation

Over a complete cycle the change in internal energy is zero because the gas returns to its initial state. The first law then gives net heat absorbed equal to net work done by the gas. The net work equals the area enclosed by the cycle on a pressure-volume diagram.

Question 43Physics

A gas undergoes an isothermal expansion at temperature T. Which statement about the gas is correct?

  1. The temperature rises as the gas expands because the molecules move faster.
  2. No heat enters or leaves the gas during the expansion.
  3. The internal energy stays constant and the gas absorbs heat equal to the work it does. Correct answer.
  4. The internal energy decreases by the amount of work done by the gas.

Explanation

For an ideal gas, internal energy depends only on temperature, so it stays constant in an isothermal process. The first law then requires the heat absorbed to equal the work done by the gas. The gas must absorb heat to maintain its temperature while expanding.

Question 44Physics

A concave mirror has a focal length of 10 cm. An object is placed 30 cm from the mirror. Where is the image formed?

  1. 15 cm in front of the mirror Correct answer.
  2. 60 cm in front of the mirror
  3. 30 cm in front of the mirror
  4. 15 cm behind the mirror

Explanation

Using the mirror equation 1/f = 1/u + 1/v with f = 10 cm and u = 30 cm gives 1/v = 1/10 − 1/30 = 1/15. The image distance is therefore 15 cm, and a positive value for a concave mirror means a real image in front of the mirror.

Question 45Physics

A step-down transformer is used to supply a low-voltage device. Which statement about an ideal transformer is correct?

  1. It reduces the voltage while the current in the secondary is correspondingly larger. Correct answer.
  2. It works with direct current as well as alternating current.
  3. It increases the power supplied to the secondary circuit.
  4. It changes the frequency of the alternating supply.

Explanation

For an ideal transformer, input power equals output power, so a voltage step-down is accompanied by a step-up in current. Transformers rely on changing magnetic flux, which requires an alternating supply. They do not change the frequency of the supply.

Question 46Physics

A radioactive source has a half-life of 12 days. A sample initially contains 8.0 × 10²⁰ atoms of the radionuclide. How many atoms remain undecayed after 36 days?

  1. 4.0 × 10²⁰
  2. 1.0 × 10²⁰ Correct answer.
  3. 2.0 × 10²⁰
  4. 6.7 × 10¹⁹

Explanation

The time of 36 days corresponds to three half-lives, since 36 ÷ 12 = 3. After each half-life the number of undecayed atoms halves, so after three half-lives it is 8.0 × 10²⁰ ÷ 8 = 1.0 × 10²⁰. Decay is random, so this is the expected number.

Question 47Physics

A satellite orbits a planet in a circular orbit of radius r. If the orbital radius is increased to 4r, what happens to the orbital speed?

  1. It is reduced to one quarter.
  2. It stays the same because the satellite's mass is unchanged.
  3. It halves. Correct answer.
  4. It doubles.

Explanation

For a circular orbit, gravitational force provides the centripetal force, giving v² = GM/r. The orbital speed is therefore proportional to 1/√r, so increasing r by a factor of four halves the speed. The satellite's own mass cancels out of the equation.

Question 48Physics

In a double-slit interference experiment, the slit separation is decreased while the wavelength and screen distance are unchanged. What happens to the fringe spacing?

  1. It decreases.
  2. It stays the same.
  3. It becomes zero.
  4. It increases. Correct answer.

Explanation

Fringe spacing is given by w = λD/d, where d is the slit separation. Decreasing d while keeping wavelength and screen distance constant increases the spacing, because the pattern spreads out. This is why closely spaced slits give widely separated fringes.

Question 49Physics

A metal surface has a work function of 2.0 eV. Light of photon energy 3.5 eV is incident on the surface. What is the maximum kinetic energy of the emitted photoelectrons?

  1. 0.57 eV
  2. 2.0 eV
  3. 1.5 eV Correct answer.
  4. 5.5 eV

Explanation

Einstein's photoelectric equation gives maximum kinetic energy as photon energy minus work function. Subtracting 2.0 eV from 3.5 eV gives 1.5 eV. The work function is the minimum energy needed to release an electron from the metal.

Question 50Physics

A particle of mass m is confined in a one-dimensional box of length L. How does the energy of its ground state change if the length of the box is doubled?

  1. It is halved.
  2. It stays the same.
  3. It is quartered. Correct answer.
  4. It is doubled.

Explanation

The allowed energies of a particle in a one-dimensional box are proportional to n²/L². For the ground state, doubling L increases L² by a factor of four, so the energy falls to one quarter of its original value. Confining a particle more tightly raises its energy.