A potential difference of 12 V is used to generate a current of 750 mA to heat water for 5 minutes. Calculate the energy transferred to the water in that time.

Electrical power = rate of doing work We know P = E/t and E = Vit Therefore: P = VI

Power

P = ? V = 120 V I = 6 A P = 720 W

An appliance running on 120 V draws a current of 6 A. Calculate the power used by this application.

Symbol: R Unit: Ohms (Ω) A measure of how hard it is for current to flow through a particular material. Yes As electrons “bump” into ions so they will need an energy boost (from the power source) to keep going. This boost needs to be greater than the resistance of the object or electrons will not flow.

Resistance

V = I R V = Potential difference (V) I = Current (A) R = Resistance (Ω)

Ohms Law for a constant temperature

V = 240 I = 10 R = ? R = 24 Ω

An electric heater draws 10 A of current when connected to a 240 V power supply. Calculate the resistance of the element in the heater.

Objects that obey ohms law. They are called resistors. Ohmic resistors are used to control the amount of current in a circuit. If the potential difference is doubled, then the current will also double. Will have straight-line V-I graphs, as they are proportional.

Ohmic conductors

Do not follow ohm’s law Do not have a straight line V-I graph. Resistance is not constant.

Non-ohmic conductors

Each component is dependant on the other (if one breaks, the circuit is broken, no flow of charge). Current is the same throughout the components of the circuit. Voltage is shared throughout the components of the circuit.

Series circuit

Allow for greater control of individual components (if one “line” breaks, the others still function). Current is shared throughout the components of the circuit. Voltage is the same throughout the components of the circuit.

Parallel circuit

Parallel, as each is provided with an equal potential difference.

Consider a scenario where you have two circuits. Each circuit has two light bulbs. Circuit A has the light bulbs connected in series, circuit B has them connected in parallel. In which circuit will the light bulbs shine brightest?

Definition: The sum of the resistance in all components within a circuit. Series: Parallel: RT = R1 + R2 + R3 etc. 1/RT = 1/R1 + 1/R2 + 1/R3 etc. Complete STAWA sets for practice.

Effective resistance

Components that can be manipulated to change the voltage across another component. Potentiometer: a sliding or turning object known as a wiper will alter the amount of resistance it provides. Thermistor: alters the amount of resistance depending on the temperature. - PTC: positive terminal coefficient, will increase resistance with temperature. - NTC: negative terminal coefficient, will decrease resistance with increased temperature.

Voltage dividers

Derived form V=IR Vout = Vin x R2/(R1 + R2)

Voltage dividers (don't need it but it's easier)

Three pins: - Active and Neutral: carries current to and from the device active: red/brown neutral: black/blue - Earth: connects the circuit through the ground. colour: green or green & yellow

Home circuits

When there is little to no resistance or no insulation between the active and neutral wires. Heat generated can cause electrical fires.

Short circuit

Interrupt the flow of current if it exceeds a set value.

Fuses and circuit breakers