Flashcards
calculating power
Flashcards do conjunto (16)
- 1define power ratingthe rate at which an appliance transfers energy, measured in joules per second or watts
- 21 Watt, W == 1 joule per second, j/s
- 3Give the formula for powerP = energy / time
- 4A 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 - 5Give the formula for power, using currentpower = current x potential difference
- 6Calculate 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 - 7Describe how a resistor workswork 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 - 8Give the formula for power supplied to a resistorpower = current^2 * resistance
- 9Give the formula for chargecurrent * time
- 10What happens when charge flows through a resistor?energy is transferred to the resistor, so the resistor becomes hotter
- 11Give the formula for energy transferred to a component.E = V * Q
- 12What is the energy from the battery transferred to?1. to the component
2. to the resistor - 13Give the formula for energyenergy = power * time
- 14How is the efficiency of a device calculated?from the power supplied to it and the useful energy it transfers
- 15efficiency == output / input (x100%)
- 16A 230V, 12A electric motor, has an efficiency of 60%, calculate the: a) power supplied to it b) output c) energy wasteda) 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
Informações
- Descrição
- • 5.3: electrical power and potential difference • 5.4: electric currents and electrical transfers • 5.5: appliances and efficiency
- Criado por
- Farha Idrees
- Visualizações
- 77
- Avaliação