KNEC Physics Paper 3 Question Paper / 2016 KCSE MOKASA Joint Examination

You are provided with the following;
• a rectangular glass block
• 4 optical pins
• a soft board
• a plain paper
Proceed as follows:
(a) Place the glass block on the plain paper with one of the largest face upper most.
Trace round the glass block using a pencil as shown below.

(b) Remove the glass block and construct a normal at B. Construct an incident ray AB of
angle of incidence, i = 20^o‍
(c) Replace the glass block and trace the ray ABCD using the optical pins.

(d) Remove the glass block and draw the path of the ray ABCD using a pencil. Measure
length L and record it in the table below.

(6 marks)
(e) Repeat the procedure above for the angles of incidence given.
(f) Calculate the value of L₂ and 1/L₂ ; Record in the table.

(g) Plot a graph of 1/L₂ (y-axis) against Sin² i .
(5 marks)

(h) Calculate the gradient, S. (3 marks)
Given that the equation of that graph is: 
(i) Determine the 1/L₂ – intercept C and the Sin² i – intercept B.
C = _______________________________________ (1 mark)
B = _______________________________________ (1 mark)
(j) Calculate the value of Q given by; (2 marks)
𝑄𝑄 𝐵𝐵
(k) Hand in your constructions on the plain paper together with the answer script.
(2 marks)

I. You are provided with the following:
• A voltmeter
• An ammeter
• A dry cell
• A cell holder
• A switch
• 7 connecting wires (4 wires with crocodile clips at one end)
• A mounted resistance wire.
(a) Connect voltmeter across the dry cell on an open circuit. Measure its e.m.f.

 (1 mark)
(b) Now connect the apparatus provided as shown below.

Place the crocodile clip/jockey on the wire AB starting with L = 20 cm. Close
the switch K. Record the terminal p.d. , V and corresponding current I.

(6 marks)
(c) Plot a graph of 1/V (y-axis) against 1/R . (4 marks)

(d) Given that the equation of graph is;
𝐸𝐸
Determine from the graph:
(i) the intercept C on 1/v – axis
C = ___________________________________ (1 mark)
and hence calculate the e.m.f. E of the cell. (2 marks)
(ii) the slope S of the graph. (2 marks)
(e) (i) Use the values of C and S above to find W, given by 𝑤𝑤W = S/C (1 mark)
(ii) What is the physical meaning of W. (1 mark)

II. You are provided with the following;
• Half-metre rule
• Knife edge (raised)
• A thread (approx. 20cm in form of a loop)
• 50g mass
(a) Determine the c.o.g of the half-metre rule.
c.o.g. = _____________________ cm mark. (1 mark)
(b)

(i) Pivot the rule at 15cm mark and balance it with the mass as shown.
When it is well balanced, note and record the position of the
50g mass; (1 mark)
Position of 50g mass = _________________ cm mark
(ii) Use your results to determine the weight of the rule. (2 marks)