A torch bulb is labelled 2.5 V, 0.3 A. Calculate the power of the bulb.

$$P = 2.5 \text{ V} \times 0.3 \text{ A}$$ $$P = 0.75 \text{ W}$$

The power of the bulb is $\boxed{\text{0.75 W}}$.

285. An electric bulb is labelled '40 W, 240 V'. Calculate:

a) the resistance of the filament used in the bulb.

$$R = \frac{(240 \text{ V})^2}{40 \text{ W}}$$ $$R = \frac{57600 \text{ V}^2}{40 \text{ W}}$$ $$R = 1440 \, \Omega$$

The resistance of the filament is $\boxed{\text{1440 } \Omega}$.

b) the current through the filament when the bulb works normally.

$$I = \frac{40 \text{ W}}{240 \text{ V}}$$ $$I = 0.1666... \text{ A}$$ $$I \approx 0.17 \text{ A}$$

The current through the filament is $\boxed{\text{0.17 A}}$.

286. A 3 kW immersion heater is used to heat water. Calculate the electrical energy converted into heat energy in 40 minutes.

$$P = 3 \text{ kW} = 3 \times 1000 \text{ W} = 3000 \text{ W}$$ $$t = 40 \text{ minutes} = 40 \times 60 \text{ s} = 2400 \text{ s}$$

$$E = 3000 \text{ W} \times 2400 \text{ s}$$ $$E = 7,200,000 \text{ J}$$

The electrical energy converted is $\boxed{\text{7,200,000 J}}$.

287. What is the power dissipated in a 6 $\Omega$ resistor when the current through it is?

The current value is missing from the question. Please provide the current to calculate the power dissipated.

288. In 5 seconds, an electric iron takes 10 000 joules of energy from the main supply. What is its power:

a) In Watts?

$$P = \frac{10000 \text{ J}}{5 \text{ s}}$$ $$P = 2000 \text{ W}$$

The power in Watts is $\boxed{\text{2000 W}}$.

b) In Kilowatts?

$$P = \frac{2000 \text{ W}}{1000}$$ $$P = 2 \text{ kW}$$

The power in Kilowatts is $\boxed{\text{2 kW}}$.

289. How much electric energy in joules does a 150 watts lamp convert to heat and light energy in:

a) 15 seconds

$$E = 150 \text{ W} \times 15 \text{ s}$$ $$E = 2250 \text{ J}$$

The energy converted is $\boxed{\text{2250 J}}$.

b) 5 seconds

$$E = 150 \text{ W} \times 5 \text{ s}$$ $$E = 750 \text{ J}$$

The energy converted is $\boxed{\text{750 J}}$.

c) 1 min

$$E = 150 \text{ W} \times 60 \text{ s}$$ $$E = 9000 \text{ J}$$

The energy converted is $\boxed{\text{9000 J}}$.

290. Define electrical power as used in electrical circuit.

Electrical power is the rate at which electrical energy is converted into other forms of energy (like heat, light, or mechanical energy) or transferred within an electrical circuit. It is measured in Watts (W).

291. Calculate the (a) current through (b) resistance of the filament of

a) a bulb rated at 240 V, 60 W

$$I = \frac{60 \text{ W}}{240 \text{ V}}$$ $$I = 0.25 \text{ A}$$

The current is $\boxed{\text{0.25 A}}$.

$$R = \frac{(240 \text{ V})^2}{60 \text{ W}}$$ $$R = \frac{57600 \text{ V}^2}{60 \text{ W}}$$ $$R = 960 \, \Omega$$

The resistance is $\boxed{\text{960 } \Omega}$.

b) an electric kettle rated at 2 kW, 240 V.

$$I = \frac{2000 \text{ W}}{240 \text{ V}}$$ $$I \approx 8.33 \text{ A}$$

The current is $\boxed{\text{8.33 A}}$.

$$R = \frac{(240 \text{ V})^2}{2000 \text{ W}}$$ $$R = \frac{57600 \text{ V}^2}{2000 \text{ W}}$$ $$R = 28.8 \, \Omega$$

The resistance is $\boxed{\text{28.8 } \Omega}$.

292. a) A washing machine is marked 240 V, 3 kW. What does this mean?

This means that the washing machine is designed to operate safely and efficiently when connected to a 240 Volt electrical supply. When operating normally, it will consume electrical energy at a rate of 3 kilowatts (3000 Watts).

b) Calculate the electrical energy consumed by this machine in 1 hour.

$$E = 3 \text{ kW} \times 1 \text{ h}$$ $$E = 3 \text{ kWh}$$

The electrical energy consumed is $\boxed{\text{3 kWh}}$.

293. a) Which bulb in Fig. below is the brightest? Explain your answer.

The figure shows bulb P (2000 $\Omega$) and bulb Q (500 $\Omega$) connected in series.

Therefore, Bulb P is the brightest because it has a higher resistance and will dissipate more power ($P = I^2 R$) for the same current flowing through it.

b) Both the bulbs in Fig. below are dimmer compared to the normal brightness, when each bulb is connected in turn to the same power supply. Why?

The bulbs are dimmer because the voltage supplied by the "same power supply" is lower than their individual rated voltage required for normal brightness. When connected in series, the voltage across each bulb is even lower than the supply voltage, making them even dimmer than if connected individually to that same supply.

294. A 2 kW immersion water heater is switched on for 3 hours. Calculate the amount of heat energy given off by the heater.

$$E = 2 \text{ kW} \times 3 \text{ h}$$ $$E = 6 \text{ kWh}$$

The amount of heat energy given off is $\boxed{\text{6 kWh}}$.

295. If an electric heater consumes a current of 4 A when connected to a 240 V supply, what is its power.

$$P = 240 \text{ V} \times 4 \text{ A}$$ $$P = 960 \text{ W}$$

The power of the heater is $\boxed{\text{960 W}}$.

296. A bulb rated 200 W is used for 12 hours. Calculate the energy it consumed in kWh.

$$E = 0.2 \text{ kW} \times 12 \text{ h}$$ $$E = 2.4 \text{ kWh}$$

The energy consumed is $\boxed{\text{2.4 kWh}}$.

297. Define a fuse and state its function in an electrical circuit.

A fuse is a safety device that contains a thin wire designed to melt and break an electrical circuit if the current exceeds a safe level. Its function is to protect electrical appliances and wiring from damage due to overcurrents or short circuits, thereby preventing fires and electrical hazards.

298. Name any four devices that have electric heating elements.

• Electric kettle
• Toaster
• Electric iron
• Immersion heater

299. How much current flows through a bulb rated 150 W when a potential difference of 240 V is supplied to the bulb when operating normally?

$$I = \frac{150 \text{ W}}{240 \text{ V}}$$ $$I = 0.625 \text{ A}$$

The current flowing through the bulb is $\boxed{\text{0.625 A}}$.

300. Explain why a magnetic compass deflects when brought near a conductor carrying current.

A magnetic compass deflects because a conductor carrying electric current produces a magnetic field around it. This magnetic field interacts with the magnetic field of the compass needle, causing the needle to align itself with the resultant magnetic field, thus deflecting from its original orientation (usually pointing north). This phenomenon is known as Oersted's discovery.

301. Define the following terms:

The terms to be defined are missing from the question. Please provide the terms you would like defined.