(a) Explain what is meant by photoelectric emission

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

(c) State four applications of photoelectric emission.

(d) In a photocell, no electrons are emitted until the threshold frequency of light is reached. Explain what happens to the energy of the light before emission of electrons begins. State one factor that may affect the number of emitted electrons. 

(a)(i) Explain what is meant by a machine (ii) Define the terms: mechanical advantage, velocity ratio and efficiency as applied to a machine. Derive the equation connecting the three terms.

(b) Explain why the efficiency of a machine is usually less than 100%

(c) A screw jack whose pitch is 4.4mm is used to raise a body of mass 8000 kg through a height of 20cm. The length of the tommy bar of the jack is 70cm. If the efficiency of the jack is 80%, calcuate the: (i) velocity ratio of the jack; (ii) mechanical advantage of the jack (iii) effort required in raising the body, (iv) work done by the effort in raising the body \((g = 10ms^{-2};  \pi = \frac{22}{7}\))

(a) With the aid of a labelled diagram, describe an experiment to illustrate the relationship between the volume and the temperature of a given mass of air at constant pressure.

(b) A uniform capillary tube of negligible expansivity sealed at one end, contains air trapped by a pellet of mercury. The trapped air column is 13.7cm long at 0°C and 18.7cm long at 100°C. Calculate the cubical expansivity of the air at constant pressure.

(c) Using the kinetic theory of gases, explain why the volume of a fixed mass of gas at constant pressure increases with increase in temperature. 
 

(a) State the laws of electromagnetic induction.

(b) Draw a labelled diagram of a simple d.c. generator and explain how it works.

(c) State three methods by which higher e.m.f. could be obtained from the generator. 

(a) Explain the following, illustrating your answer with one example in each case: (i) nuclear fusion: (ii) nuclear fission: (iii) radiation hazards.

(b) State two advantages of fusion over fission and explain briefly why, in spite of these advantages, fusion is not normally used for the generation of power.

(c) The current, I in an a.c. circuit is given by the equation: \(I = 30 sin 100\pi t\), where t is the time in seconds. Deduce the following from this equation: (i) frequency of the current (ii) peak value of the current, (iii) r.m.s value of the current.