Question

(b) A student carries out an experiment to find the specific heat capacity of aluminium. He uses

an electric heater and a thermometer inserted into separate holes in an aluminium block.

The following data are obtained.

mass of aluminium block = 2.0 kg

power of heating element = 420 W

time of heating = 95 s

initial temperature of block = 19.5 °C

final temperature of block = 40.5 °C

Answer 1

Answer:

Specific heat capacity is the (thermal) energy per unit mass required to raise the temperature of a substance by one degree

(b)

(i) To allow for the heat losses to (or gained from) the surroundings.

(ii)

{Heat energy = mass × specific heat capacity × change in temperature

H = mcΔθ

Divide by time,

H/t = mcΔθ / t

Power = (m/t)cΔθ

where H/t is the energy / time which is the power

m/t is the mass of liquids flowing through the tube per unit time (in this question it is m – see the unit from the table; it is ‘g s-1’ and not ‘g’.)

To account for the heat exchange with the surroundings, we include ±h.}

EITHER P = mcΔθ ± h

{We can obtain 2 different equations from the 2 set of readings.}

OR 44.9 = 1.58×10–3 × c × (25.5 – 19.5) ± h

OR 33.3 = 1.11×10–3 × c × (25.5 – 19.5) ± h            

{The value of h is actually unknown. BUT if we consider both equation at the same time, it can be eliminated by subtracting the 2 equations.}

(44.9 – 33.3) = (1.58 – 1.11) × 10–3 × c × (25.5 – 19.5)

c = 4100 (4110) J kg–1 K–1