(a)(i) Explain photoelectric emission.

(ii) State four applications of photoelectric emission.

(b) Draw and label a diagram showing the structure of a simple type of a photocell and explain its mode of operation.

(c) In a photocell, no electrons are emitted until the threshold frequency of light is reached.

(i) Explain what happens to the energy of the light before emission of electrons begin.

(ii) State one factor that may affect the number of emitted electrons.

You are provided with a metre rule, a knife edge, two pieces of thread and two masses m\(_{1}\) and m\(_{2}\)

1. Record the values of m\(_{1}\) and m\(_{2}\).
2. Balance the metre rule horizontally on the knife edge and record the balance point G.
3. With the knife edge at the 60 cm mark of the metre rule, suspend m\(_{1}\) at the 20 cm mark and m\(_{2}\) at a suitable mark such that the rule balances horizontally as illustrated in the diagram above.
4. Record the positions Y of m\(_{1}\) and Q of m\(_{2}\). 
5. Evaluate 1= P - Y and d = Q - P
6. Repeat the procedure for four other positions of m, at 18, 16, 14 and 12 cm marks.
7. In each case, evaluate and record l and d.
8. Tabulate your readings.
9. Plot a graph of l on the vertical axis against d on the horizontal axis.
10. Determine the slope of the graph.
11. State two precautions taken to ensure accurate results.

(b}i. With the aid of a diagram, indicate the forces acting on the metre rule in the experimental set-up above.

ii. Define moment of a force about a point and state its S.1. unit.

Using the diagram above as a guide, carry out the following instructions:

1. Fix. the drawing paper provided on the drawing board
2. Place the mirror vertically with its longer side resting on the drawing paper. Trace the outline AB of the mirror. Remove the mirror.
3. Draw a normal PQ to meet the outline at the middle Q.
4. Draw a straight line through A to meet the outline of the mirror at the right angle.
5. Trace the incident ray, Q with pins P\(_{1}\) and P\(_{2}\) so that it meets the perpendicular line through A at C such that CA=X= 1.0m.
6. Replace the mirror on its outline. Locate the images of P\(_{1}\)P\(_{2}\) through the mirror using two other pins P\(_{3}\) and P\(_{4}\) so that P\(_{3}\) and P\(_{4}\) and the images of P\(_{1}\) and P\(_{2}\) are in a straight line.
7. Remove the mirror and pins P\(_{3}\) and P\(_{4}\).
   Draw a straight line through the pin points to meet AB at Q and CA produced at D.
8. Measure and record angle ACQ as è\(_{1}\), and angle ADCQ as è\(_{2}\). Also, record the value of x. Evaluate è = (è\(_{1}\) + è\(_{2}\)), x\(^{-1}\) and tan è.
9. Repeat the procedure for four other values of x = 2.0, 3.0, 4.0 and 5.0cm. Tabulate your readings.
10. Plot a graph of tan è on the vertical axis against x on the horizontal axis.
11. Determine the slope, s, of the graph. Evaluate k = 2s
12. State two precautions taken to ensure accurate results. Attach your traces to your answer booklet.

(b)i. Distinguish between regular and diffused reflections.

ii. An object is situated 25cm in front of a plane mirror. Determine the distance of the image from the object. What is the size of the image relative to the object?

You are provided with a potentiometer x y; a jockey, J; a standard resistor, R, and other necessary apparatus.

1. Connect a circuit as shown in the diagram above.
2. Close the key. Read and record the current 10 when J is not in contact with XY.
3. Let J make contact with XY at C, such that XC = l= 25 cm. Close the key. Read and record the current l.
4. Evaluate I\(^{-1}\).
5. Repeat the procedure for four other values of I = 40, 55, 70, and 85 cm. Tabulate your readings.
6. Plot a graph of l on the vertical axis against I\(^{-1}\) on the horizontal axis.
7. From your graph, deduce the value of I when l\(^{-1}\) = 0. Evaluate \(\frac{|O}{1}\)
8. State two precautions taken to ensure accurate results.

(b)i) Explain what is meant by the potential difference between two points in an electric circuit.

ii. A piece of resistance wire of diameter 0.2m and resistance 7\(\Omega\) has a resistivity of 8.8 x 10\(^{-7}\) \(\Omega\)m. Calculate the length of the wire. [\(\pi\) = \(\frac{22}{7}\)].