Edexcel - London Examinations GCE, May 1997 - Paper 2 Question 3

1.

a) i)

The heated air has to be blown towards the ground, as hot air tends to rise up by natural convection.

a) ii)  

V = 6000 m³

m= ?

r = 1.2 kg / m³

m = r . V = 1.2 x 6000

= 4 800 kg. Answer a) ii)

a) iii)

Q = m. c. (D q )

= 4800 x 1000 x 10

= 48 000 000 J or 48 MJ Answer a) iii

 Reason:

a) iv) Since air is a bad conductor of heat energy and some heat energy is lost by conduction through glass and brick walls. (10 marks)

b)

1. Find the mass of the metal block (=m)

2. Take the initial temperature of the block from the thermometer.

3. Switch on the supply starting clock at the same time.

4. When the temperature has risen by about 5oC switch off the supply and stop the clock.

5. Take the final highest temperature reached and calculate the temperature rise or difference (= D q )

6. Take the ammeter reading (= I) and voltmeter reading (= V) during the experiment. To find the specific heat capacity use:

c = (Q) / (m. D q ) or (V. I. t ) / (m x D q ))

where V = voltmeter reading

I = ammeter reading and

t = time from the clock

Precautions:

1. Place some oil in the two holes provided for the heater and the thermometer (for good thermal contact)

2. Lag the metal block to prevent heat losses by conduction

3. Allow sufficient time before taking the final temperature. (10 marks)