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NCEA Level 3 Physics study materials
NCEA Level 3 Physics study resources

NCEA Level 3 Physics practice questions

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Question 1Physics achievement standards (Level 3)

A satellite moves in a circular orbit around Earth. Which statement correctly describes the force responsible for its centripetal acceleration?

  1. The gravitational force exerted by Earth on the satellite, directed toward Earth's centre. Correct answer.
  2. The centrifugal force acting outward, which equals the gravitational force in magnitude.
  3. The tangential velocity of the satellite, which continually redirects its motion.
  4. The normal reaction from the satellite's own structure balancing its weight.

Explanation

For a satellite in circular orbit the only significant force is gravity, and it points toward the centre of Earth, providing the centripetal force. Velocity is not a force, and in an inertial frame there is no outward centrifugal force acting on the satellite.

Question 2Physics achievement standards (Level 3)

A car rounds a flat, unbanked corner of radius 50 m. If the coefficient of static friction between tyres and road is 0.60, what is the maximum speed at which the car can take the corner without skidding? Take g = 9.8 m s⁻².

  1. 24 m s⁻¹
  2. 29 m s⁻¹
  3. 17 m s⁻¹ Correct answer.
  4. 5.4 m s⁻¹

Explanation

Friction supplies the centripetal force, so μmg = mv²/r, giving v = √(μgr) = √(0.60 × 9.8 × 50) ≈ 17 m s⁻¹. Mass cancels, so the result does not depend on the car's mass.

Question 3Physics achievement standards (Level 3)

Two point charges are separated by a distance d. If the separation is doubled while both charges are unchanged, the electrostatic force between them becomes:

  1. one quarter of the original force Correct answer.
  2. four times the original force
  3. twice the original force
  4. one half of the original force

Explanation

Coulomb's law gives F ∝ 1/d², so doubling d reduces the force by a factor of 2² = 4. The force therefore becomes one quarter of its initial value.

Question 4Physics achievement standards (Level 3)

A uniform electric field of strength 2.0 × 10³ V m⁻¹ exists between two parallel plates separated by 5.0 mm. What is the potential difference between the plates?

  1. 4.0 × 10⁵ V
  2. 2.5 × 10⁵ V
  3. 0.40 V
  4. 10 V Correct answer.

Explanation

For a uniform field, V = Ed. Substituting E = 2.0 × 10³ V m⁻¹ and d = 5.0 × 10⁻³ m gives V = 10 V. The separation must be converted to metres before multiplying.

Question 5Physics achievement standards (Level 3)

A wire of length 0.20 m carrying a current of 3.0 A lies at right angles to a uniform magnetic field of flux density 0.50 T. What is the magnitude of the magnetic force on the wire?

  1. 0.30 N Correct answer.
  2. 3.0 N
  3. 0.60 N
  4. 0.075 N

Explanation

The force on a current-carrying conductor is F = BIL sin θ. With θ = 90°, sin θ = 1, so F = 0.50 × 3.0 × 0.20 = 0.30 N.

Question 6Physics achievement standards (Level 3)

A straight wire carries a current toward the top of the page. Using the right-hand grip rule, what is the direction of the magnetic field at a point directly to the right of the wire?

  1. Toward the top of the page
  2. Toward the bottom of the page
  3. Out of the page
  4. Into the page Correct answer.

Explanation

Pointing the right thumb along the current (up the page), the fingers curl around the wire. On the right-hand side of the wire the fingers point into the page, so that is the field direction there.

Question 7Physics achievement standards (Level 3)

A coil of 200 turns and area 0.010 m² lies perpendicular to a magnetic field that increases uniformly from 0.20 T to 0.60 T in 0.40 s. What is the magnitude of the induced emf?

  1. 4.0 V
  2. 0.50 V
  3. 2.0 V Correct answer.
  4. 0.010 V

Explanation

Faraday's law gives ε = N ΔΦ/Δt, with ΔΦ = A ΔB = 0.010 × 0.40 = 4.0 × 10⁻³ Wb. Then ε = 200 × 4.0 × 10⁻³ / 0.40 = 2.0 V.

Question 8Physics achievement standards (Level 3)

A transformer has 500 turns on its primary and 50 turns on its secondary. If the primary is connected to a 240 V RMS AC supply, what is the secondary RMS voltage?

  1. 48 V
  2. 2.4 V
  3. 2400 V
  4. 24 V Correct answer.

Explanation

For an ideal transformer, V_s/V_p = N_s/N_p. Rearranging gives V_s = 240 × 50/500 = 24 V, a step-down result consistent with fewer secondary turns.

Question 9Physics achievement standards (Level 3)

In a photoelectric experiment, light of frequency 6.0 × 10¹⁴ Hz is incident on a metal with work function 1.8 eV. Using h = 6.63 × 10⁻³⁴ J s and 1 eV = 1.60 × 10⁻¹⁹ J, what is the maximum kinetic energy of the emitted electrons?

  1. 1.8 eV
  2. 0.68 eV Correct answer.
  3. 2.5 eV
  4. 0.43 eV

Explanation

Photon energy is E = hf = 6.63 × 10⁻³⁴ × 6.0 × 10¹⁴ ≈ 3.98 × 10⁻¹⁹ J ≈ 2.49 eV. Subtracting the work function gives 2.49 − 1.8 ≈ 0.68 eV, the maximum kinetic energy.

Question 10Physics achievement standards (Level 3)

Which observation from the photoelectric effect cannot be explained by the wave model of light?

  1. Light spreads out and forms diffraction patterns after passing a narrow slit.
  2. Emission occurs only above a threshold frequency, regardless of intensity. Correct answer.
  3. The light beam carries energy that can be measured with a detector.
  4. The total number of emitted electrons increases with light intensity.

Explanation

The wave model predicts that any frequency would eventually supply enough energy if intensity were high enough, so a threshold frequency is unexplained. The photon model explains it: a single photon must have energy hf at least equal to the work function.

Question 11Physics achievement standards (Level 3)

An electron is accelerated from rest through a potential difference of 500 V. What is its de Broglie wavelength? Use h = 6.63 × 10⁻³⁴ J s, m = 9.11 × 10⁻³¹ kg and e = 1.60 × 10⁻¹⁹ C.

  1. 2.4 × 10⁻¹⁰ m
  2. 1.2 × 10⁻¹² m
  3. 5.5 × 10⁻¹¹ m Correct answer.
  4. 5.5 × 10⁻⁸ m

Explanation

Kinetic energy is eV = 8.0 × 10⁻¹⁷ J, so momentum p = √(2mE) ≈ 1.21 × 10⁻²³ kg m s⁻¹. Then λ = h/p ≈ 5.5 × 10⁻¹¹ m, comparable to atomic spacing.

Question 12Physics achievement standards (Level 3)

In the Bohr model of the hydrogen atom, an electron transitions from the n = 3 level to the n = 2 level. Which statement correctly describes the emitted photon?

  1. Its frequency is independent of the energy levels involved.
  2. Its energy equals the energy of the n = 2 level alone.
  3. Its energy equals the difference between the two energy levels. Correct answer.
  4. Its wavelength is longer than that of the n = 3 to n = 1 transition.

Explanation

Each spectral line corresponds to a photon carrying exactly the energy difference between two quantised levels: E_photon = E_initial − E_final. The n = 3 to n = 2 gap is smaller than the n = 3 to n = 1 gap, so its photon has lower energy and longer wavelength.

Question 13Physics achievement standards (Level 3)

A nucleus of uranium-238 undergoes alpha decay. Which nucleus is produced?

  1. Uranium-234
  2. Thorium-234 Correct answer.
  3. Protactinium-234
  4. Radium-238

Explanation

An alpha particle is a helium nucleus with 2 protons and 2 neutrons, so the parent loses 4 in mass number and 2 in atomic number. Uranium (Z = 92) becomes thorium (Z = 90) with mass number 234.

Question 14Physics achievement standards (Level 3)

A radioactive sample has a half-life of 8.0 days. What fraction of the original nuclei remains after 32 days?

  1. 1/8
  2. 1/32
  3. 1/4
  4. 1/16 Correct answer.

Explanation

The number of half-lives is 32/8.0 = 4, and the remaining fraction is (1/2)⁴ = 1/16. Each half-life halves the number of undecayed nuclei.

Question 15Physics achievement standards (Level 3)

In a nuclear fission reaction, the total mass of the products is slightly less than the total mass of the reactants. This mass difference is primarily accounted for by:

  1. the charge of the fission fragments
  2. the kinetic energy of the fission fragments and released neutrons Correct answer.
  3. the emission of an alpha particle
  4. the binding energy of the original nucleus only

Explanation

Mass-energy equivalence, E = mc², means the mass defect appears as energy released, mostly as kinetic energy of the fragments and neutrons. This kinetic energy is converted to thermal energy in a reactor.

Question 16Physics achievement standards (Level 3)

A simple pendulum has a period of 2.0 s on Earth. If it is taken to the Moon, where the gravitational field strength is about one sixth that on Earth, its period becomes approximately:

  1. 2.0 s
  2. 4.9 s Correct answer.
  3. 0.82 s
  4. 12 s

Explanation

The period of a simple pendulum is T = 2π√(l/g), so T ∝ 1/√g. Reducing g by a factor of 6 increases T by √6 ≈ 2.45, giving about 4.9 s.

Question 17Physics achievement standards (Level 3)

A mass on a spring undergoes simple harmonic motion. At the equilibrium position, which statement about its energy is correct?

  1. Both kinetic and potential energy are zero.
  2. Both kinetic and potential energy are maximum.
  3. Kinetic energy is maximum and elastic potential energy is zero. Correct answer.
  4. Kinetic energy is zero and elastic potential energy is maximum.

Explanation

At equilibrium the displacement is zero, so the spring stores no elastic potential energy and the speed is greatest. All of the system's energy is kinetic at that point, and total mechanical energy is conserved.

Question 18Physics achievement standards (Level 3)

Two coherent light sources produce an interference pattern on a screen. Which condition produces destructive interference at a point on the screen?

  1. The two waves have equal amplitude at that point.
  2. The path difference from the two sources is an odd number of half wavelengths. Correct answer.
  3. The path difference from the two sources is a whole number of wavelengths.
  4. The two waves have different frequencies at that point.

Explanation

Destructive interference occurs when waves arrive in antiphase, which happens when the path difference is (n + ½)λ. A whole-number path difference produces in-phase waves and constructive interference.

Question 19Physics achievement standards (Level 3)

In Young's double-slit experiment, the slit separation is 0.25 mm, the slit-to-screen distance is 2.0 m, and the third-order bright fringe is 12 mm from the central maximum. What is the wavelength of the light?

  1. 1.4 × 10⁻⁷ m
  2. 1.5 × 10⁻⁶ m
  3. 5.0 × 10⁻⁷ m Correct answer.
  4. 2.0 × 10⁻⁶ m

Explanation

The fringe spacing satisfies y = nλL/d, so λ = yd/(nL) = (12 × 10⁻³ × 0.25 × 10⁻³)/(3 × 2.0) = 5.0 × 10⁻⁷ m. All lengths must be converted to metres before substitution.

Question 20Physics achievement standards (Level 3)

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

  1. Total mechanical energy of the block is conserved.
  2. Kinetic energy increases while potential energy stays constant.
  3. Gravitational potential energy is converted to thermal energy at a constant rate. Correct answer.
  4. Gravitational potential energy is converted entirely to kinetic energy.

Explanation

Constant speed means kinetic energy is unchanged, so the loss of gravitational potential energy equals the work done against friction. That energy becomes thermal energy in the block and incline.

Question 21Physics achievement standards (Level 3)

A 1200 kg car travelling at 15 m s⁻¹ collides head-on with a stationary 800 kg car and they lock together. What is their common velocity immediately after the collision?

  1. 7.5 m s⁻¹ in the original direction of the moving car
  2. 22 m s⁻¹ in the original direction of the moving car
  3. 9.0 m s⁻¹ in the original direction of the moving car Correct answer.
  4. 15 m s⁻¹ in the original direction of the moving car

Explanation

Momentum is conserved in the collision: (1200 × 15) = (1200 + 800) × v. Solving gives v = 18 000/2000 = 9.0 m s⁻¹ in the original direction.

Question 22Physics achievement standards (Level 3)

A ball of mass 0.20 kg strikes a wall horizontally at 8.0 m s⁻¹ and rebounds at 6.0 m s⁻¹. The contact time is 0.040 s. What is the magnitude of the average force exerted by the wall on the ball?

  1. 10 N
  2. 70 N Correct answer.
  3. 40 N
  4. 30 N

Explanation

Taking the initial direction as positive, the change in momentum is 0.20 × (−6.0 − 8.0) = −2.8 kg m s⁻¹. The average force magnitude is 2.8/0.040 = 70 N, and the rebound direction must be included in the velocity change.

Question 23Physics achievement standards (Level 3)

A resistor of 12 Ω and a resistor of 6.0 Ω are connected in parallel across a 12 V supply. What is the total current drawn from the supply?

  1. 0.67 A
  2. 3.0 A Correct answer.
  3. 18 A
  4. 1.0 A

Explanation

The equivalent resistance of the parallel pair is (12 × 6)/(12 + 6) = 4.0 Ω, so the total current is 12/4.0 = 3.0 A. Equivalently, the branch currents of 1.0 A and 2.0 A add to 3.0 A.

Question 24Physics achievement standards (Level 3)

A 12 V battery with internal resistance 0.50 Ω is connected to an external resistor of 5.5 Ω. What is the terminal voltage of the battery?

  1. 6.0 V
  2. 12 V
  3. 11 V Correct answer.
  4. 0.50 V

Explanation

The current is I = ε/(R + r) = 12/6.0 = 2.0 A. The terminal voltage is V = ε − Ir = 12 − (2.0 × 0.50) = 11 V, since some emf is dropped across the internal resistance.

Question 25Physics achievement standards (Level 3)

A student measures the acceleration due to gravity using a simple pendulum and obtains 9.4 m s⁻². The accepted value is 9.8 m s⁻². Which statement best describes this result?

  1. The measurement is precise if repeated values are close together, but it is inaccurate because it differs from the accepted value. Correct answer.
  2. The measurement has a percentage error of about 0.4 %.
  3. The measurement is accurate because it is close to the accepted value.
  4. The measurement must be precise because a pendulum is a reliable method.

Explanation

Accuracy refers to closeness to the accepted value, while precision refers to the spread of repeated measurements. A result of 9.4 m s⁻² differs from 9.8 m s⁻² by about 4 %, so it is inaccurate even if repeated readings agree closely.

Question 26Physics achievement standards (Level 3)

A satellite moves in a circular orbit around Earth at constant speed. Which statement correctly describes the force acting on the satellite?

  1. The gravitational force is balanced by an outward centrifugal force of equal size.
  2. The gravitational force acts toward Earth's centre and provides the centripetal force. Correct answer.
  3. The gravitational force acts tangentially, in the direction of motion.
  4. No net force acts because the satellite's speed is constant.

Explanation

For circular motion a net force must point toward the centre of the circle, and gravity toward Earth's centre supplies exactly this centripetal force. The satellite's speed is constant but its velocity direction changes continuously, so a net force is required.

Question 27Physics achievement standards (Level 3)

A force of 20 N acts at 60° to the horizontal on a box that moves 3.0 m horizontally. What work does this force do on the box?

  1. 60 J
  2. 52 J
  3. 0 J
  4. 30 J Correct answer.

Explanation

Work equals Fd cos θ, so W = 20 × 3.0 × cos 60° = 20 × 3.0 × 0.50 = 30 J. Only the component of force along the displacement transfers energy.

Question 28Physics achievement standards (Level 3)

An object of mass 2.0 kg is lifted vertically at a constant speed of 0.50 m s⁻¹ for 4.0 s. What is the gain in gravitational potential energy? Take g = 9.8 m s⁻².

  1. 4.9 J
  2. 78 J
  3. 39 J Correct answer.
  4. 9.8 J

Explanation

The height gained is v × t = 0.50 × 4.0 = 2.0 m, so ΔE_p = mgh = 2.0 × 9.8 × 2.0 = 39 J. Constant speed means the lifting force equals the weight.

Question 29Physics achievement standards (Level 3)

A car of mass 1500 kg accelerates uniformly from 10 m s⁻¹ to 25 m s⁻¹. What is the change in its kinetic energy?

  1. 169 kJ
  2. 488 kJ
  3. 394 kJ Correct answer.
  4. 281 kJ

Explanation

Kinetic energy is ½mv², so ΔE_k = ½ × 1500 × (25² − 10²) = 750 × (625 − 100) = 750 × 525 = 394 kJ. Using the difference of squares avoids errors.

Question 30Physics achievement standards (Level 3)

A ball is thrown horizontally at 12 m s⁻¹ from a cliff 45 m high. Ignoring air resistance, how far from the base of the cliff does it land? Take g = 9.8 m s⁻².

  1. 55 m
  2. 36 m Correct answer.
  3. 12 m
  4. 24 m

Explanation

Vertical fall time satisfies h = ½gt², giving t = √(2 × 45 / 9.8) ≈ 3.03 s. Horizontal distance is vt = 12 × 3.03 ≈ 36 m, since horizontal and vertical motions are independent.

Question 31Physics achievement standards (Level 3)

A 2.0 kg trolley moving at 3.0 m s⁻¹ collides with and sticks to a stationary 4.0 kg trolley. What is the speed of the combined trolleys immediately after collision?

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

Explanation

Momentum is conserved in the collision: 2.0 × 3.0 = (2.0 + 4.0) × v, so v = 6.0 / 6.0 = 1.0 m s⁻¹. Kinetic energy is not conserved because the collision is inelastic.

Question 32Physics achievement standards (Level 3)

A torque of 8.0 N m acts on a wheel with moment of inertia 2.0 kg m². What is the angular acceleration of the wheel?

  1. 16 rad s⁻²
  2. 2.0 rad s⁻²
  3. 0.25 rad s⁻²
  4. 4.0 rad s⁻² Correct answer.

Explanation

Newton's second law for rotation gives τ = Iα, so α = τ / I = 8.0 / 2.0 = 4.0 rad s⁻². The angular acceleration is directly proportional to torque and inversely proportional to moment of inertia.

Question 33Physics achievement standards (Level 3)

A flywheel of moment of inertia 0.50 kg m² spins at 20 rad s⁻¹. What is its rotational kinetic energy?

  1. 200 J
  2. 100 J Correct answer.
  3. 50 J
  4. 10 J

Explanation

Rotational kinetic energy is ½Iω² = ½ × 0.50 × 20² = 0.25 × 400 = 100 J. This mirrors the translational form ½mv² with I replacing m and ω replacing v.

Question 34Physics achievement standards (Level 3)

A satellite orbits Earth at a radius twice Earth's radius. Compared with a satellite at Earth's surface radius, its orbital speed is:

  1. the same
  2. smaller by a factor of 2
  3. larger by a factor of √2
  4. smaller by a factor of √2 Correct answer.

Explanation

Orbital speed for a circular orbit is v = √(GM/r), so speed is inversely proportional to √r. Doubling r reduces the speed by a factor of √2.

Question 35Physics achievement standards (Level 3)

A spring of spring constant 200 N m⁻¹ is stretched 0.10 m from equilibrium. What is the elastic potential energy stored?

  1. 1.0 J Correct answer.
  2. 0.50 J
  3. 20 J
  4. 2.0 J

Explanation

Elastic potential energy is ½kx² = ½ × 200 × (0.10)² = 100 × 0.010 = 1.0 J. The energy depends on the square of the extension.

Question 36Physics achievement standards (Level 3)

A particle performs simple harmonic motion with amplitude 0.20 m and angular frequency 5.0 rad s⁻¹. What is its maximum acceleration?

  1. 5.0 m s⁻² Correct answer.
  2. 25 m s⁻²
  3. 1.0 m s⁻²
  4. 0.040 m s⁻²

Explanation

Maximum acceleration in SHM is a_max = ω²A = (5.0)² × 0.20 = 25 × 0.20 = 5.0 m s⁻². Acceleration is greatest at the extremes of the motion.

Question 37Physics achievement standards (Level 3)

A wave has frequency 50 Hz and wavelength 4.0 m. What is its speed?

  1. 0.080 m s⁻¹
  2. 54 m s⁻¹
  3. 200 m s⁻¹ Correct answer.
  4. 12.5 m s⁻¹

Explanation

Wave speed is the product of frequency and wavelength: v = fλ = 50 × 4.0 = 200 m s⁻¹. This follows because one wavelength passes each point every period.

Question 38Physics achievement standards (Level 3)

Light of wavelength 600 nm passes through a single slit of width 0.30 mm. At what angle is the first minimum of the diffraction pattern observed?

  1. 0.11° Correct answer.
  2. 0.057°
  3. 0.23°
  4. 1.1°

Explanation

For a single slit, minima occur where sin θ = nλ / w. With n = 1, sin θ = 600 × 10⁻⁹ / 0.30 × 10⁻³ = 2.0 × 10⁻³, giving θ ≈ 0.11°.

Question 39Physics achievement standards (Level 3)

Two identical coherent sources emit waves in phase. At a point where the path difference is 1.5 wavelengths, the waves arrive:

  1. in antiphase, producing destructive interference Correct answer.
  2. in phase, producing destructive interference
  3. in phase, producing constructive interference
  4. in antiphase, producing constructive interference

Explanation

A path difference of an odd number of half-wavelengths (here 3 × λ/2) means the waves arrive half a cycle apart, which is antiphase. Antiphase superposition gives destructive interference.

Question 40Physics achievement standards (Level 3)

A standing wave is formed on a string fixed at both ends. Which statement about the nodes is correct?

  1. Nodes are points where the wave speed is greatest.
  2. Nodes are points where the two travelling waves have equal amplitude and same phase.
  3. Nodes are points of maximum displacement where constructive interference occurs.
  4. Nodes are points of zero displacement where destructive interference occurs. Correct answer.

Explanation

In a standing wave, nodes are fixed points of zero displacement because the two oppositely travelling waves always cancel there. Antinodes, by contrast, are points of maximum amplitude.

Question 41Physics achievement standards (Level 3)

A sound source moves toward a stationary observer. Compared with the emitted sound, the observed sound has:

  1. a lower frequency and longer wavelength
  2. a higher frequency and longer wavelength
  3. a higher frequency and shorter wavelength Correct answer.
  4. the same frequency but greater amplitude

Explanation

When the source approaches, successive wavefronts are compressed into a shorter distance, reducing the observed wavelength. Because speed is fixed relative to the medium, the shorter wavelength corresponds to a higher observed frequency.

Question 42Physics achievement standards (Level 3)

An ideal gas is compressed at constant temperature. Which statement about the gas molecules is correct?

  1. Their average kinetic energy stays the same and the pressure stays the same.
  2. Their average kinetic energy increases as the volume decreases.
  3. Their average kinetic energy decreases because the volume decreases.
  4. Their average kinetic energy stays the same while the pressure increases. Correct answer.

Explanation

For an ideal gas, average molecular kinetic energy depends only on absolute temperature, so it is unchanged at constant temperature. Reducing the volume increases collision frequency with the walls, raising the pressure.

Question 43Physics achievement standards (Level 3)

A fixed mass of ideal gas is heated at constant pressure. Which statement correctly describes the change?

  1. The volume decreases as the temperature rises.
  2. The volume increases in proportion to the Celsius temperature.
  3. The volume stays constant while the pressure rises.
  4. The volume increases in proportion to the absolute temperature. Correct answer.

Explanation

Charles's law states that at constant pressure, volume is directly proportional to absolute (kelvin) temperature. Heating therefore increases volume in proportion to T measured in kelvin.

Question 44Physics achievement standards (Level 3)

A heat engine takes in 500 J of energy from a hot reservoir and does 150 J of useful work each cycle. What is its efficiency?

  1. 30% Correct answer.
  2. 70%
  3. 15%
  4. 33%

Explanation

Efficiency is useful work output divided by heat input: 150 / 500 = 0.30, or 30%. The remaining 350 J is rejected to the cold reservoir.

Question 45Physics achievement standards (Level 3)

A point charge creates an electric field. At a point twice as far from the charge, the electric field strength is:

  1. four times its original value
  2. twice its original value
  3. one half of its original value
  4. one quarter of its original value Correct answer.

Explanation

The electric field of a point charge follows an inverse-square law, E = kQ/r². Doubling r multiplies the field by 1/2² = 1/4.

Question 46Physics achievement standards (Level 3)

Two parallel plates separated by 5.0 mm have a potential difference of 250 V between them. What is the electric field strength between the plates?

  1. 1.25 × 10³ V m⁻¹
  2. 1.25 V m⁻¹
  3. 5.0 × 10⁴ V m⁻¹ Correct answer.
  4. 2.0 × 10⁻⁵ V m⁻¹

Explanation

For uniform fields between parallel plates, E = V/d = 250 / 5.0 × 10⁻³ = 5.0 × 10⁴ V m⁻¹. The field is uniform, so this value applies throughout the region.

Question 47Physics achievement standards (Level 3)

A capacitor of capacitance 4.0 μF is charged to 12 V. How much charge is stored?

  1. 0.33 μC
  2. 48 μC Correct answer.
  3. 3.0 μC
  4. 576 μC

Explanation

Charge stored is Q = CV = 4.0 × 10⁻⁶ × 12 = 48 × 10⁻⁶ C, or 48 μC. Capacitance relates stored charge to the potential difference across the plates.

Question 48Physics achievement standards (Level 3)

A wire of resistance R is cut in half and the two halves are connected in parallel. What is the resistance of the combination?

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

Explanation

Each half has resistance R/2, and two equal resistors in parallel give half of one of them: (R/2)/2 = R/4. Parallel connection always reduces the total resistance below the smallest branch.

Question 49Physics achievement standards (Level 3)

A charged particle enters a uniform magnetic field moving parallel to the field lines. What is the magnetic force on the particle?

  1. Zero, because the velocity is parallel to the field. Correct answer.
  2. Directed along the velocity.
  3. Maximum, because the velocity is parallel to the field.
  4. Directed opposite to the velocity.

Explanation

The magnetic force is F = qvB sin θ, where θ is the angle between velocity and field. When the particle moves parallel to the field, θ = 0 and sin θ = 0, so the force is zero.

Question 50Physics achievement standards (Level 3)

A coil rotates at constant speed in a uniform magnetic field, generating an alternating EMF. At the instant the coil's plane is parallel to the field, the induced EMF is:

  1. zero, because the flux through the coil is greatest
  2. zero, because the flux through the coil is zero
  3. maximum, because the flux through the coil is greatest
  4. maximum, because the flux through the coil is changing fastest Correct answer.

Explanation

EMF depends on the rate of change of flux, not on the flux itself. When the coil plane is parallel to the field, the flux is momentarily zero but changing most rapidly, so the induced EMF is at its maximum.