gcse physics topic 2

electri

sources of potential difference:

a cell, batteries, electrical generator

what is potential difference

the energy transferred per unit charge flowing from one point to another

formula for potential difference including work done and charge

v = w/q

what is an electric current

the rate of flow of electrical charge

what is a unit of charge called

a coulomb

what is a columb

the quantity of charge that passes a fixed point per second when a current of 1a is flowing

formula for charge flow:

q = it

what is p.d

work done by a unit of charge passing through a component

formula for p.d with current and resistance

v = ir

what is ohms laq

the current through a conductor is directly proportional to the potential difference across it.(at a constant temperature)

what does filament lamp graph look like and why

it is non ohmic. the resistance of the filament lamp increases as the temperature of the filament increases. this is because as the current increases the temperature of the filament increases and the higher temperature causes the atoms in the metal lattice of the filament to vibrate more making it more difficult for the current to pass through.

why does resistance increase with temperature

becuase when temperature increases atoms vibrate faster. electric current is the flow of these electrons in a material and the electrons will collide with the vibrate atoms decreasing the current.

what does diode iv graph look like and why

examples of linear compinents

fixed resistors, wires, heating elements

non linear components examples

filament lamps, diodes and leds, ldr, and thermistors

what is a thermistor

a resistore that changes with temperature, as temp increases the resistance decreases and vice versa.

what are the applications of thermistors

they act as a temperature sensor and can automatically regulate temperatured. ovens, fire alarms, digital thermometers, boilers.

what is an ldr

a light dependant resistor

how does ldr resistance change

as light intesity increases the resistance of the ldr decreases and vice versa.

applications of ldrs

it is found in lights that switch on when it gets dark, alarm clock, light intensity meters, security lights.

current in series circuit

it is the same at all points

current in parallel circuit

the current splits at junctions

p.d in series circuit

the voltage of the power supple is shared between the componenets

p.d in parallel circuit

the voltage across each component is the same

resistors in series and why

total resistance is the sum of the resistance in each components. becuase charge has to push thorugh multiple components while flowing through the circuit.

resistors in parallel circuit and why

total resistance decreases and is less than the resistance of any of the individual components.this is because two resistors in parallel have a smaller overall resistance than just one because the charge has more than one pathway to take so only some will flow along each path.

what is a dc current

a current that is steady, constantly flowing in the same direction in a circuit, from positive to negative

what is an ac current

a current that continuously changes its direction, going back and forth around a circuit

what is mains electricity

electricity generated by powerstations and transported arounf the country through the national grid

what is the voltage and frequency of the amins current in the uk

230 v and 50 hz

what wires are in a plug

live wire, earth wire and neutral wire

what is the live wire for

carries the alternating potential difference from the mains supple to a circuit

what is the nneutral wire for

forms the opposite end of the sircuir to the live wire to complete the circuit

what is the earth wire for

acts as a safety wire to stop the appliance from becoming live

how does the earth wire help

if the live wire touches the metal case of the appliance the appliance would become live, the earth wire would then complete this circuit providing a low resistance path to the earth. this causes a surge of current in the earth wire which passes through the fuse in the circuit causing it to melt hence breaking the circuit.

what is electrical power

the rate of energy transfer or the amount of energy transferred per second

what is the formula for power

p = vi

another formula for power

p = i² r

what is the formula for energy / work done

e = pt and e = qv

what is the national grid

a system consisting of cables and trasformers linking power stations to consumers