2 - ELECTRICITY
Energy and power in circuits
Resistors -
- Produce heat when electric current passes through them
- Energy transfer which heats the resistor
- Heat increases the resistors resistance - less current will flow/greater voltage needed to produce same current
- Can cause components in circuit to melt - breaks circuit
- Fuses use melting to protect circuits - melt and break the circuit if the current gets too high
- Toasters contain coil of wire with very high resistance = heat
- Current passes through coil - temperature increases - glows and gives off infrared (heat) radiation
- Electrical power - rate at which an appliance transfers energy
- An appliance with a high power rating transfers a lot of energy in a short period of time
- Energy comes from current flowing through it
- High power rating appliance - draws a large current from the supply
ELECTRICAL POWER = CURRENT X VOLTAGE
- Most appliances show their power rating and voltage rating
- Fuses should be rated near but slightly higher than the normal operating current
- Working out fuse needed -
1kW = 1000W
I = P/V
= 1000/230
= 4.3A
Slightly higher = 5 amp fuse
Appliances transfer electrical energy -
- Current flows through component, energy is transferred
- eg: lightbulb - electrical energy transferred into light energy and (waste) heat energy
- Energy transferred depends on the current through it, the voltage supplied and how lond (s) it is on for
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