14226463
Description
Flashcards by Farha Idrees, updated more than 1 year ago
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Created by Farha Idrees
over 6 years ago
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| Question | Answer |
| define power rating | the rate at which an appliance transfers energy, measured in joules per second or watts |
| 1 Watt, W = | = 1 joule per second, j/s |
| Give the formula for power | P = energy / time |
| A 40W light bulb is switched on for 30 mins. Calculate the energy it transfers. | time = 30 * 60s = 1800s energy = power * time = 40 * 1800 = 72000 --> 72 kJ |
| Give the formula for power, using current | power = current x potential difference |
| Calculate the normal current through a 500W , 230V heater + which fuse you need. | current = power / p.d. = 500 / 230 = 2.2 A you will need a 3A fuse |
| Describe how a resistor works | work is being done by the battery, to make the ions pass through the resistor ↓ each electron collides with the vibrating metal ions of the resistor ↓ this transfers energy to the ions in the resistor ↓ the ions gain kinetic energy so vibrate more ↓ the resistor becomes hotter + heats the surroundings ↓ the energy supplied to it is dissipated to the surroundings |
| Give the formula for power supplied to a resistor | power = current^2 * resistance |
| Give the formula for charge | current * time |
| What happens when charge flows through a resistor? | energy is transferred to the resistor, so the resistor becomes hotter |
| Give the formula for energy transferred to a component. | E = V * Q |
| What is the energy from the battery transferred to? | 1. to the component 2. to the resistor |
| Give the formula for energy | energy = power * time |
| How is the efficiency of a device calculated? | from the power supplied to it and the useful energy it transfers |
| efficiency = | = output / input (x100%) |
| A 230V, 12A electric motor, has an efficiency of 60%, calculate the: a) power supplied to it b) output c) energy wasted | a) power = current * voltage = 12 * 230 = 2760W b) efficiency = 60% = 0.6 output = efficiency * input output = 0.6 * 2760 = 1660W c) energy wasted = total - output = 2760 - 1660 = 1100W |
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