JAMB Physics Past Questions & Answers - Page 398

1,986.
1,987.

2 kg of water is heated with a heating coil which draws 3.5 A from a 200 V mains for 2 minutes. what is the increase in temperature of the water?

[specific heat capacity of water = 4200 jkg -1k-1]

A.

30°

B.

25°

C.

15°

D.

10°

Correct answer is D

Electricity heat energy supplies by the heater = lvt = 3.5 x 200 x (2 x 60) = 84000j.
and this heat is supplied to the 2 kg of the water MC ∆ t = 84000
2 x 4200 x ∆ t = 84000
∴ ∆t = (84000)/8400 = 10°c
∴ increase in temp. of water = 10°c

1,989.

A clinical thermometer is different from other mercury in glass thermometers owing to

A.

the constriction on its stem

B.

the grade of mercury used in it

C.

its long stem

D.

its wide range of temperatures

Correct answer is A

No explanation has been provided for this answer.

1,990.

A piece of iron weights 250 N in air and 200 N in a liquid of density 1000 kgm-3. the volume of the iron is?

A.

5.0 x 10-2 ms-2

B.

4.5 x 10--2 ms-3

C.

2.5 x 10-2 ms-8

D.

2.0 x 10-2 ms-3

Correct answer is C

With in the air = 250N
wt. in the liquid = 200N
loss in wt. in the liquid = 250 - 200 = 50N
∴ Wt. the liquid of equal vol. of the iron = 50N
∴If the density of the liquid is 1000 lgm-3
then the volume of the liquid = (N)/D = V = (25kg)/1000 =0.025m3 = 2.5 x 10-2 m8.