TRANS- NZOIA WEST DISTRICT PHYSICS PRACTICAL QUESTIONS AND ANSWERS

TRANS- NZOIA WEST DISTRICT PHYSICS PRACTICAL QUESTIONS

PART A

1. You are provided with the following:

• A complete retort stand
  
• An optical pin
  
• A concave mirror and a holder or a lump of plasticine
  
• A cork
  
• A candle
  
• A screen
  
• A metre rule
  

You are required to estimate the focal length of the mirror. Arrange the apparatus as follows in figure 1 below:

Figure 1

a) By adjusting the clamp on the stand, move the object pin up and down until the inverted image

and pin itself appear to coincide (use – no- parallax method). Measure the distance

h = …………………………………… cm

 b) Calculate the value f given that

f= ^h/₂ —————————–  

 c) Arrange the apparatus as shown in figure 2 below

Figure 2

 d) Place the candle at a distance u = 22cm from the mirror. Move the screen along the mirror rule

until a sharp image is formed on the screen. Measure and record the image distance V

 e) Repeat the experiment with the values of u = 24cm, 26cm, 28cm and 30cm. Record your values

in table 1 below

 f) Plot a graph of magnification, m (y- axis) against image distance, v

g) Given that M = V – 1 . Determine the focal length, f

  f

PART B

You are provided with the following apparatus:-

• A lens
  
• A lens holder
  
• A white screen
  
• A metre rule
  
• Candle

Procedure

 i) Set up the apparatus as shown in figure 3 below

Figure 3

 j) Starting with u = 30cm adjust the position of the screen to obtain a sharp image of the candle.  

  Record the value of V in the table 2 below

 k) Repeat the procedure above for u = 20 cm and complete the table 2 below

 Table 2

 ii) Given that the focal length of the lens satisfies the equation, f = UV

 U+V

 Determine the average value of the focal length f

Q2. You are provided with the following:

• 2 dry cells
  
• A cell holder
  
• A torch bulb
  
• A bulb holder
  
• A voltmeter
  
• An ammeter
  
• A switch
  
• 8 connecting wires, one with a jockey and some with crocodile clips
  
• A wire attached on a metre rule or millimeter scale
  

Proceed as follows :-

 a)  i) Set up the circuit as shown in figure 4 below

Figure 4

 ii) With the jockey at P (i.e. L= 100 cm), take the voltmeter reading (v) and ammeter reading (A)

Record V and I readings in table 3 below

 iii) Repeat the procedure to take readings for L = 80 cm, 60cm, 20cm and 0 cm respectively

Record your readings in table 3 below:

Table 3

iv) What changes do you observe on the bulb as Ll decreases from P to Q ?

v) Plot a graph of voltage (v) (y- axis) against current (I)

vi) Determine the slope of graph when I = 0.226A

vii) What physical quantity is represented by the slope of the graph at any given point?  

viii) Use your graph to describe how the physical quantity in (vii) above is affected as current

increases. Explain  

b) Using some of the apparatus in a (i) above, draw a diagram you would use to determine

resistance of the wire. Explain how you determine the resistance  

TRANS NZOIA WEST DISTRICT PHYSICS PRACTICAL ANSWERS

1.  a) h= 30cm

 b) f= ^h/₂ = ³⁰/₂ = 15 cm

 c) Table of results

Accuracy = +- 0.2

• For V values award 3 marks for all values within range see accuracy above, otherwise award ½ mark for each correct
  
• For M award 2 marks for all values correct but 3 -4 values correct award 1 mark and less than 3 values correct award 0 marks
  
• N.B If a school did not use the specified focal length of the mirror it should be indicated so that candidate are not penalized
  

f) Graph on graph paper

 Axes (1 mark) – Both quantity and unit on both

 Scale (1 mark) – Simple and uniform

 Plotting (2 marks) – All points correctly plotted award 2 marks

 3 – 4 points correctly plotted (1 mark)

 Line (1 mark) line to pass in at least three correctly plotted points

NB The line MUST cut the negative part of the Y- axis for a mark

g) Gradient/ slope = ⁱ/_f

f = ^I/_slope

= 15 + 0.1 cm

 TABLE 2 RESULTS

K  i)

 ii) f = uv = 400 + 465 = 865

  u+v 40 + 45.5 85.5= 10.12cm

2.  a)  iii) Table of results  

Award ½ mark for each correct reading See accuracy above

iv) It is brighter

v) Graph on graph paper

Scale 1mark (simple and uniform)

Plotting 2 marks (each ½ mark max 4 points correctly plotted)

Axes 1 mark ( Both quantity and unit on both axes)

Curves 1 mark – passing through at least 3 correctly plotted points – No mark

for straight line

vi) Slope – DV = 1.9 – 1.5 = 13.33

DI 0.25 – 0.22

 Tangent 1mark  (Tangent line must be continuous)

vii) Electrical resistance of the bulb  

viii) – Resistance increases with increase in current  

– There is increased resistance to flow of electric current as temperature increases

 b)Resistance of wire R = V

I

  Award for R as shown above or if values have been substituted by the candidate