JAMB Physics 1995

24 reviewed questions with answers and explanations.

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Question 1

Which of the following is the dimension of pressure?

  1. ML⁻¹T⁻²
  2. MLT⁻²
  3. ML²T⁻³
  4. ML⁻³
Answer and explanation

A: ML⁻¹T⁻²

Pressure is force divided by area. Force has dimensions MLT⁻² and area L², so pressure has dimensions ML⁻¹T⁻².

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Question 2

A simple pendulum at small amplitude passes its lowest point twice per second. Find its length to two decimal places, using g =10 m/s².

  1. 0.25 m
  2. 0.45 m
  3. 0.58 m
  4. 1.00 m
Answer and explanation

A: 0.25 m

A pendulum crosses its lowest point twice per complete oscillation, so two crossings per second mean period 1 s. From T =2π√(L/g), L =10/(4π²) =0.253… m, or 0.25 m to two decimal places.

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Question 3

Three non-collinear points are O, A and B. Vector P runs from O to A, Q from O to B, and R from B to A. Which relation is correct?

  1. P = Q + R
  2. P = Q – R
  3. P = R – Q
  4. P + Q + R = 0
Answer and explanation

A: P = Q + R

Following Q from O to B and then R from B to A reaches the same endpoint as P from O to A. Therefore P =Q +R.

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Question 4

A 20 N load is held at rest by two symmetric cords, each making 30° above horizontal. Find the tension T in each cord.

  1. 10.0 N
  2. 11.8 N
  3. 20.0 N
  4. 40.0 N
Answer and explanation

C: 20.0 N

The two equal tensions each make 30° above horizontal. Horizontal components cancel, while vertical balance gives 2 T sin 30° =20 N. Since sin 30° =1/2, T =20 N.

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Question 5

When a ball rolls on a smooth level ground, the motion of its centre is

  1. Translational
  2. Oscillatory
  3. Random
  4. Rotational
Answer and explanation

A: Translational

The centre of a rolling ball moves along the ground as the ball changes position. This is translational motion; rotation describes the ball turning about its centre.

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Question 7

A 20 kg block on a smooth 30° incline is joined by a light inextensible string over a frictionless massless pulley to a hanging 30 kg mass. Use g =10 m/s². Find the acceleration magnitude.

  1. 2 m/s²
  2. 4 m/s²
  3. 6 m/s²
  4. 8 m/s²
Answer and explanation

B: 4 m/s²

The hanging weight is 30 ×10 =300 N. The 20 kg block’s downslope weight component is 20 ×10 sin 30° =100 N. The net driving force is 200 N on 50 kg, so a =4 m/s².

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Question 8

Approximate lunar surface gravity as one-sixth of Earth’s. If Earth’s gravity is 10 m/s², find lunar gravity to two decimal places.

  1. 0.10 m/s²
  2. 0.74 m/s²
  3. 1.67 m/s²
  4. 10.00 m/s²
Answer and explanation

C: 1.67 m/s²

Using the usual approximation that lunar surface gravity is one-sixth of Earth’s gives gmoon =10/6 =1.666… m/s², or 1.67 m/s².

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Question 14

A wire obeying Hooke’s law is extended by 0.02 m from its unstretched length by a final force of 500 N. Find its stored elastic energy.

  1. 5 J
  2. 10 J
  3. 10³ J
  4. 10⁴ J
Answer and explanation

A: 5 J

For a Hooke’s-law wire, force rises linearly from zero to 500 N over the 0.02 m extension. Stored energy is the triangular area under the force-extension graph:½ ×500 ×0.02 =5 J.

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Question 17

A fixed amount of air in a bubble rises slowly through a lake at constant temperature. Neglect surface-tension effects. Its volume increases because

  1. Atmospheric pressure acts on the surface of the lake.
  2. Pressure increases with depth of the lake.
  3. Density remains constant with pressure
  4. The bubble experiences an upthrust.
Answer and explanation

B: Pressure increases with depth of the lake.

Water pressure is higher at greater depth. As the bubble rises, external pressure falls. At constant temperature a fixed amount of gas expands as its pressure decreases, according to Boyle’s law.

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Question 18

In the classical ideal-gas model, absolute temperature is a measure of the

  1. Total heat transferred to the gas
  2. Mean translational kinetic energy per molecule
  3. Kinetic energy of one particular molecule
  4. Total work done by the molecules
Answer and explanation

B: Mean translational kinetic energy per molecule

For a classical ideal gas, average translational kinetic energy per molecule is 3 kT/2. Temperature therefore measures this average, rather than the energy of a particular molecule or total heat transfer.

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Question 22

An ideal 2000 W kettle heats 2.0 kg of water from 20 °C to 100 °C. Neglect kettle heat capacity and heat loss. With water’s specific heat capacity 4200 J/(kg·K), how long does this take?

  1. 420 s
  2. 336 s
  3. 168 s
  4. 84 s
Answer and explanation

B: 336 s

The temperature rise is 100 −20 =80 K. Heating needs Q =mcΔT =2.0 ×4200 ×80 =672000 J. At 2000 W, the time is 672000/2000 =336 s.

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Question 27

Which of the following is the exclusive property of a transverse wave?

  1. Diffraction
  2. Refraction
  3. Compression
  4. Polarization
Answer and explanation

D: Polarization

Polarization selects the direction of oscillation in the plane perpendicular to travel. That directional freedom belongs to transverse waves; a purely longitudinal wave oscillates along its travel direction.

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Question 28

A radio signal has wavelength 1500 m and frequency 200 kHz. At the same wave speed, what wavelength corresponds to 1000 kHz?

  1. 7 500 m
  2. 300 m
  3. 75 m
  4. 15 m
Answer and explanation

B: 300 m

The wave speed is fλ =200000 ×1500 =3 ×10⁸ m/s. At 1000000 Hz, the wavelength is 3 ×10⁸/10⁶ =300 m.

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Question 29

The difference between sound waves and light waves is that sound waves

  1. Are transverse while light waves are longitudinal.
  2. Require a medium to travel while light waves do not.
  3. Can be diffracted but light waves cannot
  4. Cannot be reflected but light waves can.
Answer and explanation

B: Require a medium to travel while light waves do not.

Sound consists of mechanical disturbances of a material medium. Light is electromagnetic radiation and can propagate through vacuum, so it does not require matter along its path.

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Question 31

For a steady simple acoustic tone, its pitch is increased primarily by

  1. Increasing the frequency
  2. Increasing the amplitude
  3. Decreasing the loudness
  4. Decreasing the intensity
Answer and explanation

A: Increasing the frequency

For a steady simple tone, a higher vibration frequency is heard as a higher pitch. Changing amplitude mainly changes loudness rather than the tone’s frequency.

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Question 32

During a total solar eclipse observed from Earth, which arrangement holds?

  1. Earth is between the Moon and Sun
  2. Sun is between the Moon and Earth
  3. Moon is between the Sun and Earth
  4. The ozone layer is threatened
Answer and explanation

C: Moon is between the Sun and Earth

During a total solar eclipse, the Moon lies between the Sun and Earth. An observer in the Moon’s umbra sees the entire bright solar disc covered; the alignment and apparent size must also be suitable.

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Question 36

Which of the following pairs of colours gives the widest separation in the spectrum of white light?

  1. Red and violet
  2. Green and yellow
  3. Red and indigo
  4. Yellow and violet.
Answer and explanation

A: Red and violet

Red and violet occupy opposite ends of the visible spectrum. Their separation spans the full listed colour range, exceeding any pair with an endpoint nearer the middle.

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Question 37

Parallel plates are 8.0 ×10⁻³ m apart at a potential difference of 600 V, with the negative plate earthed. Neglect edge effects. Find the electric-field magnitude.

  1. 4.8 V/m
  2. 75.0 V/m
  3. 4800.0 V/m
  4. 75000.0 V/m
Answer and explanation

D: 75000.0 V/m

Away from the edges, the uniform field between parallel plates has magnitude E =V/d. Thus E =600/(8.0 ×10⁻³) =75000 V/m. It points from the positive plate to the earthed negative plate.

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Question 38

Which statement best describes Earth’s magnetic field at different surface locations?

  1. The same in magnitude and direction
  2. The same in magnitude but different in direction
  3. Different in both magnitude and direction
  4. Different in magnitude but not in direction.
Answer and explanation

C: Different in both magnitude and direction

Earth’s magnetic field varies geographically in strength and direction. Its inclination and declination, as well as its magnitude, depend on location.

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Question 39

A resistor’s resistance is halved and its applied voltage tripled. Find the ratio of its new current to its original current.

  1. 1:6
  2. 1:3
  3. 2:1
  4. 6:1
Answer and explanation

D: 6:1

Ohm’s law gives I =V/R. Tripling voltage and halving resistance gives Inew =3 V/(R/2) =6 V/R, so the new-to-old current ratio is 6:1.

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Question 40

A battery of emf 12 V and internal resistance 0.5 Ω is connected across a cable of resistance 1.0 Ω. Find the current.

  1. 16.0 A
  2. 8.0 A
  3. 0.8 A
  4. 0.4 A
Answer and explanation

B: 8.0 A

The battery’s internal resistance is in series with the cable. Total resistance is 0.5 +1.0 =1.5 Ω, giving I =12/1.5 =8.0 A.

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Question 43

A capacitor network between two terminals has these sections in series: 2 μF, 3 μF, a parallel pair of 2 μF and 4 μF, then 4 μF. Find the equivalent capacitance.

  1. 15.0 μF
  2. 9.8 μF
  3. 1.3 μF
  4. 0.8 μF
Answer and explanation

D: 0.8 μF

The parallel pair gives 2 +4 =6 μF. The four series sections are 2,3,6 and 4 μF, so 1/C =1/2 +1/3 +1/6 +1/4 =1.25 μF⁻¹. Therefore C =0.8 μF.

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Question 45

The maximum voltage magnitude across a 100 Ω resistor is 20 V. Find its maximum instantaneous power.

  1. 5.00 W
  2. 4.00 W
  3. 2.00 W
  4. 0.25 W
Answer and explanation

B: 4.00 W

Instantaneous resistor power is p =v²/R. When the voltage magnitude reaches 20 V, its maximum power is 20²/100 =4 W.

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Question 47

An ideal transformer has 400 primary turns and 100 secondary turns. With 12 V AC applied to the primary, what is the secondary voltage, using the same voltage convention?

  1. 3 V
  2. 6 V
  3. 24 V
  4. 48 V
Answer and explanation

A: 3 V

An ideal transformer has voltage ratio equal to turns ratio. The secondary voltage is 12 ×100/400 =3 V, making this a step-down transformer.

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