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GTLE Subject Specialism Physics study materials
GTLE Subject Specialism Physics study resources

GTLE Subject Specialism Physics practice questions

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Question 1Mechanics and Motion

A cyclist travels 240 m in 40 s along a straight road. What is the cyclist's average speed?

  1. 9.6 m/s
  2. 0.17 m/s
  3. 6 m/s Correct answer.
  4. 4 m/s

Explanation

Average speed is total distance divided by total time, so 240 m ÷ 40 s = 6 m/s. This is a scalar quantity and describes the rate of covering distance regardless of direction.

Question 2Mechanics and Motion

Which of the following statements about a body moving with constant velocity is correct?

  1. It covers unequal displacements in equal time intervals.
  2. Its speed changes but its direction remains fixed.
  3. It has zero acceleration and covers equal displacements in equal time intervals. Correct answer.
  4. Its acceleration increases uniformly with time.

Explanation

Constant velocity means both magnitude and direction of velocity are unchanged, so acceleration is zero. A zero-acceleration motion covers equal displacements in equal time intervals by definition.

Question 3Mechanics and Motion

A stone is dropped from rest and falls freely under gravity. Ignoring air resistance, what is its speed after 3.0 s? (Take g = 9.8 m/s².)

  1. 29.4 m/s Correct answer.
  2. 3.0 m/s
  3. 44.1 m/s
  4. 9.8 m/s

Explanation

For free fall from rest, v = gt, so v = 9.8 m/s² × 3.0 s = 29.4 m/s. The speed increases linearly with time because acceleration due to gravity is constant.

Question 4Mechanics and Motion

Which quantity is a vector?

  1. Time
  2. Speed
  3. Displacement Correct answer.
  4. Distance

Explanation

A vector has both magnitude and direction; displacement specifies how far and in which direction an object has moved. Distance, speed and time are scalars, having magnitude only.

Question 5Mechanics and Motion

A car accelerates uniformly from 10 m/s to 30 m/s in 5.0 s. What is its acceleration?

  1. 8.0 m/s²
  2. 2.0 m/s²
  3. 6.0 m/s²
  4. 4.0 m/s² Correct answer.

Explanation

Acceleration is the change in velocity divided by the time taken: (30 − 10) m/s ÷ 5.0 s = 4.0 m/s². Uniform acceleration means this rate is constant over the interval.

Question 6Mechanics and Motion

A force of 12 N acts on a 3.0 kg mass on a frictionless surface. What is the resulting acceleration?

  1. 36 m/s²
  2. 15 m/s²
  3. 0.25 m/s²
  4. 4.0 m/s² Correct answer.

Explanation

Newton's second law gives a = F/m, so a = 12 N ÷ 3.0 kg = 4.0 m/s². The acceleration is in the same direction as the net applied force.

Question 7Mechanics and Motion

Two forces act on a point: 8 N to the east and 6 N to the north. What is the magnitude of the resultant force?

  1. 10 N Correct answer.
  2. 14 N
  3. 2 N
  4. 48 N

Explanation

The two forces are perpendicular, so the resultant magnitude is found by the Pythagorean theorem: √(8² + 6²) = √100 = 10 N. Perpendicular vectors add in quadrature, not by simple arithmetic.

Question 8Mechanics and Motion

A book rests on a horizontal table. Which statement correctly describes the reaction to the book's weight, according to Newton's third law?

  1. The reaction is the weight of the table acting on the floor.
  2. The reaction is the friction between the book and the table.
  3. The reaction is the normal force of the table on the book.
  4. The reaction is the gravitational pull of the book on the Earth. Correct answer.

Explanation

Newton's third law pairs act on different bodies: the Earth pulls the book down, so the book pulls the Earth up with an equal and opposite force. The normal force is a separate contact force that balances the weight but is not its reaction pair.

Question 9Mechanics and Motion

A block slides down a plane inclined at 30° to the horizontal. Taking g = 9.8 m/s² and ignoring friction, what is the acceleration of the block along the incline?

  1. 0 m/s²
  2. 4.9 m/s² Correct answer.
  3. 9.8 m/s²
  4. 8.5 m/s²

Explanation

The component of gravitational acceleration along the incline is g sin θ, so a = 9.8 × sin 30° = 9.8 × 0.5 = 4.9 m/s². The normal force cancels the perpendicular component of weight, leaving only the parallel component to accelerate the block.

Question 10Mechanics and Motion

An object moves in a horizontal circle at constant speed. Which statement about its acceleration is correct?

  1. The acceleration is zero because the speed is constant.
  2. The acceleration points away from the centre and equals v²/r.
  3. The acceleration points toward the centre and equals v²/r. Correct answer.
  4. The acceleration is directed tangentially and increases the speed.

Explanation

Although the speed is constant, the direction of velocity changes continuously, producing a centripetal acceleration of magnitude v²/r directed toward the centre of the circle. This centripetal acceleration is what changes the direction of motion.

Question 11Mechanics and Motion

A ball is projected horizontally at 15 m/s from a cliff 20 m high. Taking g = 9.8 m/s² and ignoring air resistance, how far horizontally from the base does it land?

  1. 30 m Correct answer.
  2. 15 m
  3. 45 m
  4. 20 m

Explanation

The fall time from rest vertically is t = √(2h/g) = √(40/9.8) ≈ 2.0 s. The horizontal distance is then x = vₓt = 15 × 2.0 ≈ 30 m, since horizontal and vertical motions are independent.

Question 12Mechanics and Motion

A 5.0 kg box is pulled across a rough floor by a horizontal force of 30 N while a friction force of 10 N acts on it. What is the acceleration of the box?

  1. 4.0 m/s² Correct answer.
  2. 8.0 m/s²
  3. 6.0 m/s²
  4. 2.0 m/s²

Explanation

The net force is the applied force minus friction: 30 N − 10 N = 20 N. Dividing by mass gives a = 20 N ÷ 5.0 kg = 4.0 m/s², so the acceleration follows the net force, not the applied force alone.

Question 13Mechanics and Motion

A body of mass 4.0 kg moving at 3.0 m/s collides and sticks to a stationary body of mass 2.0 kg. What is their common velocity after the collision?

  1. 4.5 m/s
  2. 2.0 m/s Correct answer.
  3. 3.0 m/s
  4. 1.5 m/s

Explanation

Momentum is conserved in a perfectly inelastic collision: (4.0 × 3.0) = (4.0 + 2.0) × v. Solving gives 12 = 6.0v, so v = 2.0 m/s.

Question 14Mechanics and Motion

A force of 50 N stretches a spring by 0.20 m within its elastic limit. What is the spring constant?

  1. 250 N/m Correct answer.
  2. 0.004 N/m
  3. 10 N/m
  4. 100 N/m

Explanation

Hooke's law states F = kx, so k = F/x = 50 N ÷ 0.20 m = 250 N/m. The spring constant measures the stiffness of the spring and is constant within the elastic limit.

Question 15Mechanics and Motion

A wheel starting from rest reaches an angular velocity of 20 rad/s in 4.0 s with constant angular acceleration. What is the angular displacement during this time?

  1. 20 rad
  2. 5 rad
  3. 40 rad Correct answer.
  4. 80 rad

Explanation

For constant angular acceleration from rest, θ = ½(ω₀ + ω)t = ½(0 + 20)(4.0) = 40 rad. This mirrors the linear kinematic relation for average velocity over a uniform acceleration interval.

Question 16Mechanics and Motion

A uniform metre rule is pivoted at its centre and is in equilibrium. A 2.0 N weight hangs 30 cm to the left of the pivot. Where must a 3.0 N weight be placed to balance the rule?

  1. 15 cm to the left of the pivot
  2. 30 cm to the right of the pivot
  3. 45 cm to the right of the pivot
  4. 20 cm to the right of the pivot Correct answer.

Explanation

For rotational equilibrium the moments about the pivot must be equal: 2.0 N × 30 cm = 3.0 N × d. Solving gives d = 60/3.0 = 20 cm, so the 3.0 N weight must be 20 cm to the right.

Question 17Mechanics and Motion

A 60 kg person climbs a vertical flight of stairs 4.0 m high in 8.0 s. Taking g = 10 m/s², what average power is developed against gravity?

  1. 240 W
  2. 2400 W
  3. 300 W Correct answer.
  4. 30 W

Explanation

Work done against gravity is mgh = 60 × 10 × 4.0 = 2400 J. Average power is work divided by time: 2400 J ÷ 8.0 s = 300 W.

Question 18Mechanics and Motion

A ball of mass 0.50 kg is thrown vertically upward with 20 J of kinetic energy. Taking g = 10 m/s² and ignoring air resistance, what maximum height does it reach?

  1. 2.0 m
  2. 20 m
  3. 10 m
  4. 4.0 m Correct answer.

Explanation

At the maximum height all kinetic energy becomes gravitational potential energy: mgh = 20 J. Thus h = 20 ÷ (0.50 × 10) = 4.0 m, illustrating conservation of mechanical energy.

Question 19Mechanics and Motion

A car of mass 1200 kg rounds a flat horizontal curve of radius 50 m at 15 m/s. What is the minimum coefficient of static friction needed to prevent skidding?

  1. 0.90
  2. 0.45 Correct answer.
  3. 0.20
  4. 0.30

Explanation

The required centripetal force is provided by friction: μmg = mv²/r, so μ = v²/(rg) = 225 ÷ (50 × 9.8) ≈ 0.46, closest to 0.45. Friction must supply exactly the centripetal force for the car to follow the curve without slipping.

Question 20Mechanics and Motion

A projectile is launched at 40 m/s at 30° above the horizontal on level ground. Taking g = 10 m/s² and ignoring air resistance, what is its horizontal range?

  1. 80 m
  2. 139 m Correct answer.
  3. 120 m
  4. 160 m

Explanation

The range on level ground is R = v² sin 2θ / g = 1600 × sin 60° ÷ 10 ≈ 1600 × 0.866 ÷ 10 ≈ 139 m. This formula assumes equal launch and landing heights and no air resistance.

Question 21Mechanics and Motion

Two masses, 3.0 kg and 1.0 kg, are connected by a light string over a frictionless pulley. Taking g = 10 m/s², what is the acceleration of the system?

  1. 2.5 m/s²
  2. 7.5 m/s²
  3. 10 m/s²
  4. 5.0 m/s² Correct answer.

Explanation

The net driving force is the weight difference (3.0 − 1.0) × 10 = 20 N, and the total mass accelerated is 4.0 kg. Thus a = 20 ÷ 4.0 = 5.0 m/s², the standard Atwood-machine result.

Question 22Mechanics and Motion

A 2.0 kg object moving at 6.0 m/s collides elastically head-on with a stationary 4.0 kg object. What is the velocity of the 2.0 kg object immediately after the collision?

  1. 0 m/s
  2. −2.0 m/s (reversed) Correct answer.
  3. 2.0 m/s in the original direction
  4. 4.0 m/s in the original direction

Explanation

For a head-on elastic collision, v₁' = ((m₁ − m₂)/(m₁ + m₂))v₁ = ((2.0 − 4.0)/6.0) × 6.0 = −2.0 m/s. The negative sign shows the lighter object rebounds, reversing its direction.

Question 23Mechanics and Motion

A satellite orbits a planet in a circular orbit. If the orbital radius is doubled while the planet's mass stays constant, how does the orbital speed change?

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

Explanation

For a circular orbit, gravitational force provides the centripetal force: GMm/r² = mv²/r, giving v = √(GM/r). Doubling r therefore reduces v by a factor of √2.

Question 24Mechanics and Motion

A body of mass 2.0 kg experiences a net force that varies with time, delivering an impulse of 12 N·s. If the body starts from rest, what is its final speed?

  1. 3.0 m/s
  2. 12 m/s
  3. 6.0 m/s Correct answer.
  4. 24 m/s

Explanation

Impulse equals change in momentum: J = mΔv, so Δv = 12 N·s ÷ 2.0 kg = 6.0 m/s. Since the body starts from rest, this change equals the final speed.

Question 25Mechanics and Motion

A uniform rod of length 2.0 m is pivoted at one end and held horizontally before being released. Taking g = 9.8 m/s², what is its initial angular acceleration? (Moment of inertia about the end is mL²/3.)

  1. 7.4 rad/s² Correct answer.
  2. 9.8 rad/s²
  3. 14.7 rad/s²
  4. 4.9 rad/s²

Explanation

The torque about the pivot is mg(L/2), and τ = Iα with I = mL²/3. Thus α = (mgL/2)/(mL²/3) = 3g/(2L) = 3 × 9.8 ÷ 4.0 ≈ 7.4 rad/s².

Question 26Mechanics and Motion

A cyclist moves along a straight road with velocity increasing uniformly from 4.0 m/s to 12 m/s in 8.0 s. What distance does the cyclist travel in this interval?

  1. 32 m
  2. 128 m
  3. 64 m Correct answer.
  4. 96 m

Explanation

For uniform acceleration the average velocity is the mean of the initial and final velocities, (4.0 + 12)/2 = 8.0 m/s. Multiplying by the time interval gives 8.0 × 8.0 = 64 m. This is equivalent to applying s = (u + v)t/2 with consistent units.

Question 27Mechanics and Motion

Which quantity is defined as the rate of change of displacement with respect to time and therefore carries both magnitude and direction?

  1. Acceleration
  2. Distance travelled
  3. Average velocity Correct answer.
  4. Average speed

Explanation

Velocity is the vector rate of change of displacement with time, so it has both magnitude and direction. Speed is the scalar rate of change of distance, and acceleration is the rate of change of velocity rather than of displacement.

Question 28Mechanics and Motion

A stone is thrown vertically upward at 20 m/s from the top of a 25 m high cliff. Taking g = 10 m/s² and ignoring air resistance, how long does the stone take to reach the ground below?

  1. 4.0 s
  2. 2.0 s
  3. 5.0 s Correct answer.
  4. 7.0 s

Explanation

Taking upward as positive, the displacement to the ground is s = −25 m, with u = +20 m/s and a = −10 m/s². Solving −25 = 20t − 5t² gives 5t² − 20t − 25 = 0, i.e. t² − 4t − 5 = 0, so t = 5 s or t = −1 s; only the positive root is physical.

Question 29Mechanics and Motion

A box of mass 8.0 kg rests on a horizontal floor. A horizontal force of 20 N is applied, but the box remains stationary. Taking g = 9.8 m/s², what is the magnitude of the static friction force acting on the box?

  1. 0 N
  2. 78 N
  3. 20 N Correct answer.
  4. 98 N

Explanation

While the box remains at rest the horizontal forces must balance, so static friction equals the applied horizontal force, 20 N. The normal force of 78 N sets only the maximum possible friction, μsN, which need not be reached.

Question 30Mechanics and Motion

A moving trolley of mass 3.0 kg collides head-on with a stationary trolley of mass 1.0 kg. After the collision the 3.0 kg trolley continues at 1.0 m/s and the 1.0 kg trolley moves at 6.0 m/s in the same direction. What was the initial speed of the 3.0 kg trolley?

  1. 6.0 m/s
  2. 4.0 m/s
  3. 2.0 m/s
  4. 3.0 m/s Correct answer.

Explanation

Total momentum is conserved in the collision, so 3.0u = 3.0 × 1.0 + 1.0 × 6.0 = 9.0 kg·m/s. Dividing by 3.0 kg gives u = 3.0 m/s, consistent with the stated directions.

Question 31Mechanics and Motion

A flywheel of moment of inertia 0.40 kg·m² is acted on by a constant net torque of 2.0 N·m. Starting from rest, what is its angular displacement after 3.0 s?

  1. 45 rad
  2. 7.5 rad
  3. 22.5 rad Correct answer.
  4. 90 rad

Explanation

The angular acceleration is α = τ/I = 2.0/0.40 = 5.0 rad/s². Using θ = ½αt² with zero initial angular velocity gives θ = 0.5 × 5.0 × 9.0 = 22.5 rad.

Question 32Mechanics and Motion

A satellite moves in a circular orbit around a planet. Which single change would increase the satellite's orbital period by the largest factor?

  1. Tripling the orbital radius while keeping the planet's mass fixed Correct answer.
  2. Halving the satellite's mass while keeping the orbit unchanged
  3. Doubling the orbital radius while keeping the planet's mass fixed
  4. Doubling the planet's mass while keeping the orbital radius fixed

Explanation

Kepler's third law gives T² ∝ r³/M, so T ∝ r^(3/2) and the period is independent of satellite mass. Tripling r multiplies T by 3^1.5 ≈ 5.2, whereas doubling r multiplies it by only about 2.8. Doubling the planet's mass reduces the period by a factor of √2.

Question 33Waves, Sound and Optics

A sound wave travels through air with a frequency of 500 Hz. If the speed of sound in air is 340 m/s, what is the wavelength of the wave?

  1. 170 m
  2. 0.34 m
  3. 0.68 m Correct answer.
  4. 1.47 m

Explanation

The wave equation v = fλ relates speed, frequency and wavelength. Rearranging gives λ = v/f = 340/500 = 0.68 m. The wavelength is the distance the wave advances in one full oscillation.

Question 34Waves, Sound and Optics

Which property of a sound wave determines its pitch as perceived by a listener?

  1. Its amplitude
  2. Its intensity
  3. Its speed of propagation
  4. Its frequency Correct answer.

Explanation

Pitch is the perceptual correlate of frequency: higher frequency sounds are heard as higher pitch. Amplitude and intensity relate to loudness, while propagation speed is set by the medium rather than the pitch.

Question 35Waves, Sound and Optics

Light travelling in air strikes a flat glass surface at an angle of incidence of 40°. Which statement correctly describes the refracted ray?

  1. It bends away from the normal because glass is denser than air.
  2. It is totally internally reflected at any angle of incidence.
  3. It bends toward the normal because glass has a higher refractive index than air. Correct answer.
  4. It continues straight through without changing direction.

Explanation

Snell's law states n₁sinθ₁ = n₂sinθ₂. Since glass has a higher refractive index than air, sinθ₂ is smaller than sinθ₁, so the ray bends toward the normal. Total internal reflection only occurs going from denser to less dense media beyond the critical angle.

Question 36Waves, Sound and Optics

In a transverse wave, the particles of the medium oscillate in which direction relative to the direction of energy propagation?

  1. Perpendicular to propagation Correct answer.
  2. Randomly in all directions
  3. Parallel to propagation
  4. At 45° to propagation

Explanation

By definition, in a transverse wave the displacement of the medium is perpendicular to the direction in which the wave travels. Light and waves on a string are transverse. Longitudinal waves, such as sound in air, have displacement parallel to propagation.

Question 37Waves, Sound and Optics

A plane mirror forms an image of a real object. Which set of characteristics correctly describes the image?

  1. Real, inverted, magnified
  2. Real, upright, same size
  3. Virtual, inverted, diminished
  4. Virtual, upright, same size, laterally inverted Correct answer.

Explanation

A plane mirror produces an image that appears behind the mirror at the same distance as the object, so it is virtual and cannot be projected on a screen. It is upright and the same size as the object, but left and right are reversed (lateral inversion).

Question 38Waves, Sound and Optics

A wave has a period of 0.25 s. What is its frequency?

  1. 0.25 Hz
  2. 25 Hz
  3. 2.5 Hz
  4. 4 Hz Correct answer.

Explanation

Frequency is the reciprocal of period: f = 1/T. With T = 0.25 s, f = 1/0.25 = 4 Hz. This means four complete oscillations occur each second.

Question 39Waves, Sound and Optics

Which region of the electromagnetic spectrum has the longest wavelength?

  1. X-rays
  2. Radio waves Correct answer.
  3. Ultraviolet
  4. Gamma rays

Explanation

The electromagnetic spectrum ordered by increasing wavelength is gamma rays, X-rays, ultraviolet, visible, infrared, microwave, radio. Radio waves occupy the longest-wavelength end, with wavelengths from millimetres to kilometres.

Question 40Waves, Sound and Optics

Two coherent sources emit sound of the same frequency and are a distance apart such that a point is equidistant from both. What is observed at that point?

  1. No interference pattern because the sources are coherent
  2. A beat frequency equal to the source frequency
  3. Complete destructive interference with zero amplitude
  4. Constructive interference with maximum amplitude Correct answer.

Explanation

At a point equidistant from two coherent in-phase sources, the path difference is zero, so the waves arrive in phase. They interfere constructively, producing a maximum amplitude. Beats require two slightly different frequencies.

Question 41Waves, Sound and Optics

A double-slit experiment uses light of wavelength 600 nm. The slit separation is 0.30 mm and the screen is 2.0 m away. What is the fringe spacing on the screen?

  1. 4.0 mm Correct answer.
  2. 0.40 mm
  3. 2.0 mm
  4. 0.90 mm

Explanation

Fringe spacing is given by Δy = λD/d. Substituting λ = 6.0×10⁻⁷ m, D = 2.0 m and d = 3.0×10⁻⁴ m gives Δy = (6.0×10⁻⁷ × 2.0)/(3.0×10⁻⁴) = 4.0×10⁻³ m, or 4.0 mm.

Question 42Waves, Sound and Optics

A convex lens of focal length 10 cm forms an image of an object placed 30 cm from the lens. Where is the image formed and what is its nature?

  1. 15 cm on the same side, virtual and upright
  2. 15 cm on the opposite side, real and inverted Correct answer.
  3. 20 cm on the opposite side, real and inverted
  4. 30 cm on the opposite side, real and upright

Explanation

Using 1/f = 1/u + 1/v with f = 10 cm and u = 30 cm: 1/v = 1/10 − 1/30 = 2/30, so v = 15 cm. A positive image distance for a converging lens means a real image on the opposite side, and it is inverted.

Question 43Waves, Sound and Optics

A pipe closed at one end resonates at its fundamental frequency of 200 Hz. What is the frequency of the next higher resonant mode?

  1. 400 Hz
  2. 300 Hz
  3. 800 Hz
  4. 600 Hz Correct answer.

Explanation

A pipe closed at one end supports only odd harmonics: f, 3f, 5f, and so on. The next mode above the fundamental 200 Hz is the third harmonic, 3 × 200 = 600 Hz. Even harmonics are absent because a node and antinode must fit the pipe.

Question 44Waves, Sound and Optics

A sound source moves toward a stationary observer. How does the observed frequency compare with the emitted frequency?

  1. It is unchanged because the observer is stationary.
  2. It is lower because the wavelength is stretched.
  3. It is higher because the speed of sound increases.
  4. It is higher because the wavelength is compressed. Correct answer.

Explanation

As the source approaches, successive wavefronts are emitted from progressively closer positions, compressing the wavelength in front of the source. Since the speed of sound in the medium is unchanged, the shorter wavelength corresponds to a higher observed frequency.

Question 45Waves, Sound and Optics

Unpolarised light passes through two ideal polarising filters whose transmission axes are at 60° to each other. What fraction of the incident intensity emerges?

  1. 1/2
  2. 1/4
  3. 3/4
  4. 1/8 Correct answer.

Explanation

The first filter transmits half the unpolarised intensity, giving I₀/2. The second filter obeys Malus's law, transmitting cos²60° = 1/4 of that. The final intensity is therefore (1/2)(1/4) = 1/8 of the incident intensity.

Question 46Waves, Sound and Optics

A ray of light travels from water (n = 1.33) into air. What is the critical angle for total internal reflection?

  1. 41°
  2. 24°
  3. 37°
  4. 49° Correct answer.

Explanation

The critical angle satisfies sinθc = n₂/n₁ = 1.00/1.33 = 0.752. Taking the inverse sine gives θc ≈ 48.8°, which rounds to 49°. Beyond this angle, total internal reflection occurs.

Question 47Waves, Sound and Optics

Which statement about the relationship between the speed, frequency and wavelength of a wave crossing from one medium into another is correct?

  1. Frequency stays constant and wavelength changes with speed. Correct answer.
  2. Speed stays constant and frequency changes.
  3. Both frequency and wavelength stay constant.
  4. Wavelength stays constant and frequency changes with speed.

Explanation

The frequency of a wave is set by the source and does not change when the wave enters a new medium. Since v = fλ, a change in wave speed must be accompanied by a change in wavelength. Refraction of light into a denser medium shortens the wavelength.

Question 48Waves, Sound and Optics

An object is placed between a converging lens and its focal point. What type of image is produced?

  1. Virtual, upright and magnified Correct answer.
  2. Real, inverted and diminished
  3. Real, inverted and magnified
  4. Virtual, upright and diminished

Explanation

When the object distance is less than the focal length, the lens equation gives a negative image distance, indicating a virtual image on the same side as the object. The magnification is greater than one, so the image is upright and magnified, like a magnifying glass.

Question 49Waves, Sound and Optics

Two tuning forks of frequencies 256 Hz and 260 Hz are sounded together. What beat frequency is heard?

  1. 2 Hz
  2. 516 Hz
  3. 130 Hz
  4. 4 Hz Correct answer.

Explanation

The beat frequency equals the difference between the two frequencies: 260 − 256 = 4 Hz. The listener hears a loudness variation four times per second as the waves alternately reinforce and cancel.

Question 50Waves, Sound and Optics

In a Young's double-slit experiment, the whole apparatus is immersed in water (n = 1.33) instead of air. How does the fringe spacing change?

  1. It stays the same because frequency is unchanged.
  2. It doubles because the wavelength doubles.
  3. It increases by a factor of 1.33.
  4. It decreases by a factor of 1.33. Correct answer.

Explanation

In water the wavelength of the light is reduced to λ/n, since the frequency is fixed but the speed is lower. Fringe spacing Δy = λD/d is directly proportional to wavelength, so it decreases by a factor of n = 1.33.