Electricity

what is insulation?

plastic around wire, doesn’t conduct so when you touch insulation your safe

what is double insulation?

mains sealed in plastic box so if it contains any electrical fault and you touch appliance, your safe

what is earthing?

• earth wire connects mains in house with ground

• if fault in appliance, earth wire provides low resistance route for current to travel to earth

what is a fuse?

thin wire in a box, if it gets too hot it melts and the circuit is broken

where are fuses?

in the plug

what do fuses protect?

protects house form fires + appliances

what are circuit breakers?

resettable fast cut off triggered by power surge

where are circuit breakers?

on entry to house

what do circuit breakers protect?

everything

why does current in a resistor cause a temperature increase?

• collisions between electrons and metal ions transfers some energy to the thermal store of the metal

• the extra energy makes the metal hot

how is the heating effect of current used in homes?

heaters or kettles

state the relationship between power, current and voltage

P = IV

what does P = IV allow us to calculate?

• rate of energy supply to circuit (cells, batteries)

• rate of energy use in circuit (bulbs, resistors)

state the relationship between power, energy, and time

P = E / t

state the relationship between energy transferred, current, voltage, and time

E = IVt

what is direct current?

current always flows in 1 direction

where do we get direct current from?

cells, batteries, solar panels

what is alternating current?

current direction constantly changing between forwards + backwards

where do we get alternating current from?

main sockets and generators

describe the direct current graph

straight line (voltage doesn’t change)

describe the alternating current graph

wave

why are parallel circuits more appropriate for domestic lighting?

• if series circuit breaks, whole circuit doesn’t work (all lights out)

• if parallel circuit breaks, other branches still work (all other lights work)

what is the relationship between voltage and current?

voltage increases = current increases

what is the relationship between resistance and current? (refer to number of components)

more components = more resistance = current decreases

what is ohms law?

• current + voltage are directly proportional

• graph is straight line through origin

how does current and voltage vary in metal filament lamps (bulbs)?

• as voltage increases, the filament heats up

• hot filament → more resistance

• current increases but slowly

how does current and voltage vary in diodes?

• component that only lets current flow one way

• non-ohmic

describe the patterns in a IV graph for metal filament lamps (bulbs)

• non linear → not ohmic

• steeper curve = lower resistance

• shallow curve = higher resistance

describe the patterns in a IV graph for diodes

• non-ohmic

• very steep = very low resistance

• flat = massive resistance

how to investigate how current and voltage vary in metal filament lamps (bulbs) and diodes experimentally?

1. set up circuit with cell, ammeter in series, voltmeter in parallel, variable resistor

2. change the voltage using the variable resistor

3. measure current and voltage each time

4. plot an I-V graph

relationship between current and resistance

• resistance increases = current decreases

• resistance decreases = current increases

relationship between resistance and light intensity in an LDR

resistance decreases with light intensity

relationship between resistance and temperature in a thermistor

resistance decreases with temperature

how do lamps and LEDs indicate a presence of current?

they show current flowing through a circuit because they light up

state the formula linking voltage, current and resistance

I = V/R

what is current?

current is the rate of flow of charge

state the formula linking charge, time and current

Q = It

what is electric current in solid metallic conductors?

electric current in solid metallic conductors is a flow of negatively charged electrons

(if confused see to notes page spec point 2.16)

why is current conserved at a junction in a circuit?

because charge is always conserved (electric charge can’t be created or destroyed)

fill in the blanks!

the voltage across 2 components connected in —— are ——

the voltage across 2 components connected in parallel are equal

how to calculate currents, voltages and resistances of two resistive components connected in a series circuit?

• current in series is equal everywhere

• voltage in series is split between components

• calculate total resistance with formula, do answer subtract the resistance of one component = resistance of other component

what is voltage and what a volt is?

• voltage is the energy transferred per unit charge passed (V = E/Q)

• a volt is a joule per coulomb

state the formula linking energy transferred, charge and voltage

E = QV