JAMB Physics Past Questions & Answers - Page 11

51.

Which of the following thermometers measures temperature from the thermal radiation emitted by objects?

A.

Pyrometer thermometer

B.

Platinum resistance thermometer

C.

Thermocouple thermometer

D.

Constant pressure gas thermometer

Correct answer is A

A pyrometer is a type of remote-sensing thermometer used to measure the temperature of a surface. It does this by measuring the thermal radiation or infrared energy being emitted from the object. Therefore, a pyrometer thermometer measures temperature from the thermal radiation emitted by objects.

52.

What is the amount of heat required to raise the temperature of a 0.02 kg of ice cube from \(-10^oC\) to \(10^oC\) ?

[specific latent heat of fusion of ice = 3.34 x \(10^5\)  \(Jkg^-1\), Specific heat capacity of water = 4200 \(Jkg^-1\) \(k^-1\)  

Specific heat capacity of ice = 2100 \(Jkg^-1\) \(k^-1\)

A.

6680 J

B.

1680 J

C.

7520 J

D.

7940 J

Correct answer is D

Quantity of heat required to raise the temperature of the ice cube from \(-10^oC\) to \(0^oC\)
⇒H=mc►ø = 0.02 × 2100 × 0 -(-10)

⇒ H = 0.02 × 2100 × (0 + 10) = 0.02 × 2100 × 10

⇒ H = 420 J

quantity of heat required to melt ice at \(0^oC\)

⇒ H = mL = 0.02 × 3.34 × \(10^5\)

⇒H=6680 j

Quantity of heat required to raise the temperature of the melted ice cube (water) from \(0^oC\) to \(-10^oC\)

⇒H=mc►ø = 0.02 × 4200 × (10-0)

⇒H = 0.02 × 4200 × 10

⇒H = 840j

;420 + 6680 + 840 = 7940 j

 

53.

A parallel plate capacitor separated by an air gap is made of \(0.8m^2\) tin plates and 20 mm apart. It is connected to 120 V battery. What is the charge on each plate?
Take \(ε_o\) = \(8.85×10^-12 Fm^-1\)

A.

3.54nC

B.

42.5nC

C.

35.4nC

D.

4.25nC

Correct answer is B

A= \(0.8m^2\)    d= 20mm =\(\frac{20}{1000}\) = 0.02m

v =120v;  \(ε_oA\)= \(8.85 × 10^-12 fm^-1\)

C = \(\frac{ε_oA}{d}\)

C =\(\frac{8.85 × 10^-12×0.8}{0.02}\)

C= \(3.54 × 10^-10 F\)

Q= CV

⇒  \(3.54 × 10^-10\) × 120 = \(4.25×10^-8c\)

     Q=\(42.5 × 10^-9c\)  = 42.5nC

      

54.

An air bubble of radius 4.5 cm initially at a depth of 12 m below the water surface rises to the surface. If the atmospheric pressure is equal to 10.34 m of water, the radius of the bubble just before it reaches the water surface is

A.

6.43 cm

B.

8.24 cm

C.

4.26 cm

D.

5.82 cm

Correct answer is D

\(r_1\) = 4.5cm , \( P_1\) =is the total pressure on the bubble at a depth of 12m from the surface.

\(P_1\) = 12 + 10.34 =22.34m

 \(V_1\) = \(\frac{4}{3}\)π× \(r^3_1\)

= \(\frac{4}{3}× π×{4.5^3cm^3}\)

\(P_2\) = 10.34m

\(V_2\)  = \(\frac{4}{3} {π}{r^3_2}\)

from boyles law:

\(P_1V_1\)  = \(P_2V_2\) 

⇒ 22.34× \(\frac{4}{3}× π×{4.5^3}\) = 10.34 × \(\frac{4}{3}×π×{r^3_2}\)

⇒ 22.34 × \(4.5^3\) = 10.34 × \(r^3_2\)

 \(r^3_2 = \sqrt[3]{196.88}\)

⇒ \(r_2\) = 5.82cm

55.

An air bubble of radius 4.5 cm initially at a depth of 12 m below the water surface rises to the surface. If the atmospheric pressure is equal to 10.34 m of water, the radius of the bubble just before it reaches the water surface is

A.

6.43 cm

B.

8.24 cm

C.

4.26 cm

D.

5.82 cm

Correct answer is D

\(r_1\) = 4.5cm , \( P_1\) =is the total pressure on the bubble at a depth of 12m from the surface.

\(P_1\) = 12 + 10.34 =22.34m

 \(V_1\) = \(\frac{4}{3}\)π× \(r^3_1\)

= \(\frac{4}{3}× π×{4.5^3cm^3}\)

\(P_2\) = 10.34m

\(V_2\)  = \(\frac{4}{3} {π}{r^3_2}\)

from boyles law:

\(P_1V_1\)  = \(P_2V_2\) 

⇒ 22.34× \(\frac{4}{3}× π×{4.5^3}\) = 10.34 × \(\frac{4}{3}×π×{r^3_2}\)

⇒ 22.34 × \(4.5^3\) = 10.34 × \(r^3_2\)

 \(r^3_2 = \sqrt[3]{196.88}\)

⇒ \(r_2\) = 5.82cm