Physics Paper 3 WASSCE (SC), 2016

Question 2B

 

(i)         Define heat capacity


(ii)        An electric kettle rated 1.2 kW is used to heat 800 g of water initially at a temperature of 20 0C. Neglecting heat losses, calculate the time taken for the kettle to heat the water to its boiling point.
[Take boiling point of water = 101 0C, specific heat capacity of water = 4200 J kg-1 K-1].

 

Observation

 Part (b) Candidates’ responded poorly in this part as many candidates were defining specific heat capacity in place of heat capacity.

The expected answers are that candidates should:

              -          Measure and record in cm3 five values of v                               
-          Measure and record five values of m correctly evaluated to g
-          Initial temperature0 measured and recorded in oC
-          Measure and record five values of1 in oC and in trend
-          Correctly evaluate five values of 1o)
-          Show composite table containing at least v, m, 1 and

  •  Plot a graph using reasonable scale
  • Draw line of best fit
  • Determine the slope of the graph
  • Evaluate k  = 
  • State any two of the following precautions

           
e.g       -     Avoided splashing of water

        • Stirred continuously (for even distribution of heat)
        • Avoided parallax error on the thermometer/measuring cylinder
        • Repeated readings shown on table
        • Ensured the heated mass was gently dropped into the beaker

b(i)       Heat Capacity

             Is the quantity of heat required to raise the temperature of a substance by 1K or 1oC

(ii)        Pt    =   mc                                                                                                          

1200 x t =   x 4200 (101 – 20)                                                  

t =    

               =      226.8 secs.