​The figure below shows the path of a ray of light passing through a rectangular glass block placed in air

​Calculate the refractive index of glass (2mks)

​The figure below shows an object placed in front of a concave mirror. By use of correct ray diagram, locate the position of image

Solution

The figure bellows shows a wave profile for a wave whose frequency is 2HZ

Solution

​The figure below shows two parallel magnets with unlike poles adjacent to each other. Sketch the magnetic field pattern around the magnets (2mks)

Solution

​(a) Define Radio-activity (2mks)

​(b) When carrying out experiments with radioactive substances the source should never be held with bare hands but with forceps. Explain? (1mk)

​(i) Plot on the graph paper provided the graph of the count rate (y-axis) against time

A graph of count Rate against time(s)

​(ii) From the graph, determine the half-life of Radon-220 (1mk)

​(e) The diagram in the figure below shows paths taken by three radiations A,B and C from a radioactive isotope through an electric field.

​(i) State the charge on plate Y (1mk)

​(ii) Identify the radiations A and C (2mks)

​(iii) Give a reason why C deviates more than A (1mk)

(a) A 240v mains transformer  has 800 turns in the primary and N turns in the secondary. It is used to supply energy to a 12v/21w lamp. ​

The circuit above shows a step-down transformer used to light a lamp of resistance.

​Calculate.

​(a) State two advantages of a C.R.O as a voltmeter

​(b) A television tube is a cathode ray tube modified. State two modifications

​(c) State the functions of the following parts of a C.R.O

​(d) A modern X-ray tube is shown below

​(i) Name the parts labeled A-D (2mks)

​(ii) Give the functions of:- (1mk)

​(a) Define doping (1mk)

​(b) Distinguish between a p-type and n-type semi conductors (2mks)

​(c) Using a diagram illustrate a forward P-N junction (2mks)

​(d) The figure below shows a bridge circuit 

A capacitor has been connected across the resistor as shown

​(i) Sketch of the figure below the wave form when a CRO is connected across the resistor, R

​(ii) On the same axes, sketch a wave form when C.R.O is connected across R when the capacitor has been removed (1mk)

​(a) Explain why bulbs in along corridor are not wired in series (2mks)

​(b) An electric cooker has an oven rated 2500w, a grill rated 1500w and two plates each of 1000W. This cooker operates directly from 240v supply. What is the costs of operating all the parts at once for 30 minutes if electricity costs sh.10.00 per unit? (3mks)

​(c) Study the figure below

​(i) What name is given to the fitting in the diagram (1mk)

​(ii) Identify the parts labeled (2mks)

Give two advantages of a circuit breaker instead of a fuse in domestic  wiring (2mks)

​State the conditions for generation of e.m.f from a magnet (2mks)

​The following is a part of a radio-active series

​Identify the radiation r, find the values of c and d (3mks)

r

c

d

​State two uses of optical fibres whose working relies on total internal reflection (2mks)

​Give a reason why gases are poor transmitters of sound (1mk)

​Other than penetrating powers, state two differences between soft and hard X-rays (2mks)

Complete the ray diagram to show how it travels after striking the two mirrors and find the angle of reflection on each surface (2mks)

Solution

​(a) The diagram in the figure below represents a wheel and axle used as a machine, whose efficiency is 80% to raise 400N of building materials. The wheel and axles have diameters of 75cm and 15cm respectively.

The diagram in the figure below represents a wheel and axle used as a machine, whose efficiency is 80% to raise 400N of building materials. The wheel and axles have diameters of 75cm and 15cm respectively.

​(i) Mark on the diagram the correct position and direction of the load to be lifted (1mk)

​(ii) Name the principle on which this machine works (1mk)

​(iii) Calculate the effort needed to raise the load (3mks)

​(iv) The machine is operated manually and raises the load to a height of 5m in 20 seconds. Calculate the power developed by the operator (2mks)

(b)
​(i) State two factors that determines the efficiency of an inclined plane as a machine (2mks)

​(ii) Explain how these factors affect efficiency (2mks)

​Explain what you understand by each of the following terms: 

(​i) Angular velocity (1mk)

​(ii) Centripetal force (1mk)

​b) A bicycle wheel with radius 28cm moves with a linear velocity of 8m/s, determine 

​(i) the angular velocity of the wheel (2mks)

​(ii) the centripetal acceleration of a point on the rim of the wheel (2mks)

​(c) To determine the relationship between angular velocity w and tension T, a student used a smooth disc with a hole at the centre,  a string and cylindrical object of mass m, as shown below

To determine the relationship between angular velocity w and tension T, a student used a smooth disc with a hole at the centre, a string and cylindrical object of mass m, as shown above

​Describe how the student went about determining the relationship, specifying any other necessary material or instrument not shown in the diagram (3mks)

A student set-up the apparatus as shown above to determine the power of an electric heater

(a)
​(i) Other than time, state the measurements that would be used to determine the quantity of heat P absorbed by ice in a unit time (2mks)

​(ii) Complete the circuit to show the connection of the essential circuit components (2mks)

​(iii) Describe how the student would proceed to determine P (3mks)

​(iv) Give a reason why P may not be equal to the value indicated by the manufacturer (1mk)

The readings tabulated below shows how the length of a helical spring varied with the load hanging on it

(a)
​(i) Complete the table to show the values of extension (2mks)

​(ii) Draw a graph of extension (y-axis) against load for the spring (5mks)

​(ii) Determining form the graph the proportionality constant of the spring (2mks)

​(b) Two springs Q and R have proportionality constants 20N/M and 25N/M respectively. Q weighs 0.2 N while the weight of R is negligible. The two springs are arranged to support a load of 3.0N as shown in the diagram below

Determine the extension in 
(i)  Q……………………………………………..(1mk)

ii)  R ……………………………………………(1mk)

​(c) State two factors that determine the proportionality constant of a helical spring (2mks)

The diagram below shows two trolleys, A and B connected to each other by an elastic strip of negligible mass. The trolleys are pulled apart on a smooth plane till tension in the elastic strip is 4.0N and are then released suddenly

​(a) State with reason the total momentum of the trolleys when they are just released (2mks)

​(b) Calculate the initial acceleration of trolley A when released (3mks)

​(d) Which trolley covers a longer distance before collision? Explain (2mks)

​(e) Explain why the elastic strip may not stretch to the same original length after impact (2mks)

A student holds a sheet of paper at an end so that it hangs in the position A as shown above

​Explain why the paper rises to the position B when the student blows  air in the direction shown by the arrow (2mks)

Two objects made of the same material and having the same mass are heated to a temperature of 35 degrees Centigrade above that of the atmosphere and then allowed to cool in still air for 30 minutes. State one factor that will determine their final temperature (1mk)

​The figure below shows a sheet of material with the shape of an isosceles triangle. Mark its centre of gravity accurately showing how you arrive at the answer (1mk)

Problem

Solution