These three are connected to 240V main supply :
Grill = 6A
Desk lamp = 0.6A
Convector heater = 4.5
a(ii) which of these has the greatest resistance ? Explain how you can tell.
(ii) calculate the resistance of the grill
(iii) calculate the power rating of the convector heater
(b) the plug fitted to the convector heater has three wires : live,neutral,earth.
(i) which wire in the plug has no current passes in normal circumstances. Explain the safety of this wire.
(ii) why is it important that the wire connecting the heater to the main supply have a low resistance?
Someone will be happy to critique your thoughts. The three apliances are wired in parallel to the 240 V supply. Because of Ohm's Law, current is inversely proportional to resistance.
Take it from there.
The subject is physics, not physic. A physic is a laxative.
(i) To determine which device has the greatest resistance, we can use Ohm's Law, which states that resistance (R) is equal to voltage (V) divided by current (I). In this case, since all devices are connected to the same 240V main supply, we need to compare the current values.
The device with the greatest resistance will have the lowest current flow, as resistance and current are inversely proportional. Therefore, the device with the lowest current rating will have the highest resistance.
Comparing the current ratings provided:
- Grill: 6A
- Desk lamp: 0.6A
- Convector heater: 4.5A
We can see that the desk lamp has the lowest current rating (0.6A), which means it has the highest resistance among the three devices.
(ii) To calculate the resistance of the grill, we need to use Ohm's Law: R = V / I.
Given:
- Voltage (V): 240V
- Current (I): 6A
Plugging these values into the formula, we can calculate the resistance of the grill:
R = 240V / 6A
R = 40Ω
Therefore, the resistance of the grill is 40 ohms.
(iii) To calculate the power rating of the convector heater, we can use the formula: Power (P) = Voltage (V) * Current (I).
Given:
- Voltage (V): 240V
- Current (I): 4.5A
Plugging these values into the formula, we can calculate the power rating of the convector heater:
P = 240V * 4.5A
P = 1080W
Therefore, the power rating of the convector heater is 1080 watts.
(b) The plug fitted to the convector heater has three wires: live, neutral, and earth.
(i) In normal circumstances, the earth wire in the plug has no current passing through it. The purpose of the earth wire is to provide a safe return path for electric current in case of a fault, such as an electrical leakage or insulation failure. When a fault occurs, the earth wire ensures that the excess current flows directly to the ground, protecting the user from electric shock. This wire is essential for safety, as it prevents the transmission of electric current through conductive surfaces, reducing the risk of electrocution.
(ii) The wire connecting the heater to the main supply should have a low resistance for several reasons. Firstly, a low resistance wire minimizes power loss due to resistive heating. When current flows through a wire with high resistance, energy is wasted as heat. By having a low resistance wire, more of the electrical energy can be efficiently delivered to the convector heater.
Additionally, a low resistance wire can handle higher currents without heating up excessively, reducing the risk of the wire melting, causing a short circuit, or even starting a fire. It ensures that the wire can safely carry the required current from the main supply to the heater without significant voltage drops or overheating.