(a) The metal part of the machine should be earthed to neutralize any unbalanced charges developed.
(b) The leaf collapses. ✓1
The electrons flows from the ground and discharges at the sharp point. ✓1

.

Its an intrinsic semiconductor to which some impurities have been added (doping) to enhance conductivity.(1mk)

T= 2s
f = 1/T = ½ = 0.5Hz 2mk

Use: Sterilization✓1
Source: Radioactive materials 1mk

As the thermistor is heated, its resistance reduces thereby increasing its conductivity. The thermistor draws more current through it hence less current flows through the bulb B.1mk

After every 10 years half the mass decays.

1/R = 1/9+1/9+1/9 =3/9✓1
R = 9/3 = 3Ω✓1

This is when the zinc plate get ‘eaten’ away when the cell is working ✓1mk
It is minimized by use of pure zinc or coating it with mercury(amalgamation).✓1mk

If the conductor carrying current is grasped in the right hand thumb pointing a long the wire in direction of conventional current the fingers will point in the direction of the magnet (1mk)

(c)
(i) rectification is a process of converting alternating current to direct current ;
(ii) during one half cycle, A is at higher potential relative to F;
Diodes D4 and D2 are forward biased. Current flows from A- B –D4 –R2-D2 to F;
During the next half cycle, F is at a higher potential relative to A;
Diodes D3 and D1 are forward biased. Current flows from F- E- D3 –R – D1 –B –A ;
(iii) a capacitor can be connected across the output resistor R;

(b) (i)
− lamps are placed in series instead of parallel
− fuse and switch is on the neutral instead of live
(ii)
− fuse is made of a wire with low m.p.
− it safeguards the appliance against damage should the current flowing through it exceed the safe
limit.
(c)
− use high voltage
− use thick copper wires
(d) (i) a.c. generator
(ii) increasing the speed of rotation
using a stronger magnet
(iii)

ii) This is the time taken by a radioactive substance to decay by half.
b)
i) It allows the radiation into the casing1
ii) The bromine gas causes quenching effect so that it reduces secondary ionization.1
iii) The radiation enters through the mica window. It causes ionization1postive ion move to the cathode while negative ions move to the anode. A pulse current flows which is measured by scalar or rate meter

(a) (4 Marks)
− Correct diagrams.
− It occurs when the earth is between the sun and moon and all lie on a straight line.
− The earth casts a shadow on the moon.
(b) For security reasons since they cover a wide field of view.

(c)

(d)