JAMB Physics Past Questions & Answers - Page 71

351.

Temperature is the property of a body which is proportional to the ____.

A.

total kinetic energy of its molecules

B.

average kinetic energy of its molecules

C.

average speed of its molecules

D.

maximum speed of its molecules

Correct answer is B

The last postulate of the kinetic molecular theory states that the average kinetic energy of a gas particle depends only on the temperature of the gas. Thus, the average kinetic energy of the gas particles increases as the gas becomes warmer

352.

What flows to the positively charged conductor by connecting it to the earth?

A.

Electrons

B.

Ion

C.

Neutron

D.

Proton

Correct answer is A

Earth acts as a ground of zero potential. So when a positively charged conductor is connected to the earth, positive charge flows into the earth and as a result, electrons flow from earth to the conductor.

353.

An electric heating coil rated at 1Kw is used to heat 2kg of water for 2 minutes. The initial water temperature is 30\(^o\)C. Taking the specific heat of the water as 4,000Jkg \(^{-1}\) and neglecting that of the container, the final water temperature is

A.

15.0\(^o\)C

B.

45.0\(^o\)C

C.

52.5\(^o\)C

D.

60.0\(^o\)C

Correct answer is B

  Time = 2mins = 2 × 60 = 120secs

  Energy = power × time

  1000 × 120 = 120,000J

  Energy = mc(θ\(_2\) – θ\(_1\))

  120,000 = 2 × 4000(θ\(_2\) – θ\(_1\))

  θ2 = 30 + 15 = 45 \(^o\) C

354.

A beam of light is incident from air to water at an angle of 30\(^o\). Find the angle of refraction if the refractive index of water is 4/3

A.

15\(^o\)

B.

18\(^o\)

C.

22\(^o\)

D.

24\(^o\)

Correct answer is C

X = \(\frac{4}{3}\) r = ?

  Shell’s law:.  = \(\frac{Sin i^0}{ Sin r^0}\)

  = \(\frac{Sin 30^0}{Sin r^0}\)

  Sin\(r^0\) = \(\frac{3 Sin 30^0}{4}\)

  Sin \(r^0\) = 0.375

  R \(^o\) = Sin-1 (0.375)

  R \(^o\) = 22.02 \(^o\)

  R \(^o\) = 22 \(^o\)

355.

The resistance of a 40W car head lamp, drawing current from a 12V battery is ____.

A.

0.3Ω

B.

3.3Ω

C.

3.6Ω

D.

4.8Ω

Correct answer is C

Power delivered to head lamp = \(\frac{V_2}{R}\)

  = 40W

  R = \(\frac{V_2}{40}\)

  = \(\frac{(12 × 2)}{40}\)

  = 3.6Ω