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JAMB Physics Past Questions & Answers - Page 325

1,621.

A 500W heater is used to heat 0.6kg of water from 25^oC to 100^oC in t₂ seconds. If another 1000W heater is used to heat 0.2kg of water from 10^oC to 100^oC in t, seconds, find $\frac {t_1}{t_2}$

5/4

1/5

View answer & explanation

Correct answer is B

Heat energy = Electrical energy

mc $\theta$ = power x time

0.6 x c x (100 - 25) = 500 x t₁

and, 0.2 x c x (100 - 10)= 100 x t₂
$\frac {t_1}{t_2}$ = 5

1,622.

A gas has a volume of 100cm³ at 27^oC. If it is heated to temperature T until a final volume of 120cm³ is attained, calculate T

33^oC

60^oC

87^oC

114^oC

View answer & explanation

Correct answer is C

$\frac {V_1}{T_1}$ = $\frac {V_2}{T_2}$

$\frac {100}{27 + 273}$ = $\frac {120}{T + 273}$

T = 87^oC

1,623.

The linear expansivity of brass is 2 x 10^-5C^-1. If the volume of a piece of brass is 15.00cm³ at 0⁰C, What is the volume at 100^oC?

16.03cm³

16.00cm³

15.09cm³

15cm³

View answer & explanation

Correct answer is C

linear expansivity = $\frac {V_2 - V_1}{V_1 {\times} {\Delta}{\theta}}$

3 x 2 x 10^-5 = $\frac {V_2 - 15}{15 {\times} (100 - 0)}$

V₂ = 15.09cm³

1,624.

A platinum resistance thermometer records 3.0 $\Omega$ at 0^oC and 8.0 $\Omega$ at 100^oC. If it records 6.0 $\Omega$ in a certain environment, The temperature of the medium is

80^oC

60^oC

50^oC

30^oC

View answer & explanation

Correct answer is B

8 $\Omega$ .....100^oC

6 $\Omega$ ..... $\theta$ ^oC

3 $\Omega$ .....0^oC

$\frac{6 - 3}{8 - 3}$ = $\frac{\theta - 0}{100 - 0}$

therefore, $\theta$ = 60^oC