(i)

Earthing is the transfer of electrical charges from the atmosphere directly to the earth through a wire buried in the ground. This is done to conduct excess charges/current on an appliance safely to earth or to prevent the user of the appliance from getting electric shock or to protect the circuit breaker/fuse/electrical appliances

(ii)

Sources of electric power generation

1. Battery/Cell
2. Solar
3. Wind
4. Biogas
5. Nuclear
6. Hydro/water
7. Diesel

(i)

Ohm's law states that the current flowing through a metallic conductor at a constant temperature is proportional to the potential difference across it.

OR

V = IR,
where V = voltage or P.d
      I = current,
      R = resistance.

(ii)

V = IR

Current(I) = 10 A
Resistance(R) = 12.5 Ω

Potential difference/voltage = 10 x 12.5 V = 125 V

(i)

How static electricity is produced

Materials repeatedly in contact with one another/materials rubbing against one another result in the transfer of electrons from one material to another. The negatively charged material accumulates electrons over the period of contact to constitute static electricity/imbalance of electric charge.

(ii)

Sources of electric power generation apart from hydro and thermal

1. Nuclear
2. Solar
3. Wind
4. Tidal
5. Biogas/natural gas
6. Fossil/coal/oil

(i)

Power (P) = 100 W

Voltage = 240 V

Current = $\frac{\mathrm{100\; W}}{\mathrm{240\; V}}$ = 0.417 A

(ii)

Method I

P = 100 W
I = 0.417 A

100 = 0.417² x R

R = $\frac{100}{{0.417}^2}$ = 575.079504742 ≈ 575 Ω

Method II

Voltage = 240 V
Current = 0.417 A

Resistance = $\frac{\mathrm{240\; V}}{\mathrm{0.417\; A}}$ = 575.5395683 ≈ 575.5 Ω

(i)

Power = IV
where I = current and V = voltage

Current = $\frac{\mathrm{Power}}{\mathrm{Voltage}}$

Power = 1.5 kW = 1.5 x 10³ W = 1500 W

Voltage = 240 V

Current = $\frac{\mathrm{1500\; W}}{\mathrm{240\; V}}$ = 6.25 A

(ii)

Power = $\frac{\mathrm{Work\; done/Energy}}{\mathrm{Time}}$

Energy = Power x Time

Method I

Energy in kW h

Energy = 1.5 kW x 2 h = 3 kW h

Method I

Energy in Joules (J)

Note: the SI unit of time is seconds (s) hence convert the hours to seconds.

Time = 2 x 60 x 60 s = 7200 s

Energy = 1500 W x 7200 s = 1.08 x 10⁷ J

(i)

(ii)

$\frac{1}{\mathrm{R}}$ = $\frac{1}{3}$ + $\frac{1}{3}$

$\frac{1}{\mathrm{R}}$ = $\frac{2}{3}$

Cross multiply

2 x R = 1 x 3

R = $\frac{3}{2}$ = 1.5 Ω

(iii)

Voltage = 4.5 V

Resistance = 1.5 Ω

Current(I) = $\frac{4.5}{1.5}$ = 3 A

(c)