physics chapter 9 ocr a

What is p.d. Measured in

volts

What is the base units for volts

Kgm^2s^-3A^-1

What makes charge flow

EMF or electromotive force

What is EMF?

An energy transfer from another form than electricity which is normally the source like a battery

What is potential difference

The potential difference between two points is the amount of electrical energy being converted into other forms of energy (work is being done on these charge carriers)

How should a voltmeter be connected in a circuit to measure a component

In parrell

How did old style computer monitors and televisions work

They use an electron gun

What is thermionic expansion

When a piece of metal is heated to a high temperature negatively charged electrons bubble out the surface

What often happens to the electrons after thermionic expansion

They usually are attracted back to the surface as it becomes positively charged after the electrons are lost

What two equations can be used to calculate the kinetic energy of the electrons in a electron gun if the cathode has negligible kinetic energy

Work done (QV = eV = W)

eV= ½ mv²

eV = work done on electron

Q = coloumb

V = volts

Kinetic energy ( eV = 1/2 mv^2)

How does a linear particle accelerator work

Uses a alternating emf and a series of increasing size of drift tubes

Where is the electric field in a electron gun / particle accelerator

Between the drift tubes

When do the electrons accelerate and what is between these

Between the drift tubes and this is where the electric field is located

What is a resistor

A component that requires work to push the electrons to get them to flow

What's the unit for resistance and what's its base units

An ohm (kg.m^2.s^-3.A^-2)

What is ohms law

For a metallic conductor kept at constant temperature the current in the wire is directly proportional to the potential difference across it

What do fixed resistors look like on a I-V curve

They are a straight line through the origin

What does a filament bulb look like on a I-V graph

It is a non ohmic conductor as the curve is curved and the gradient decreases as you move away from the origin and it also has to pass through the origin

The graph is also symmetrical on the line y=-x

On a I-v graph what does the resistance of a high and low gradient represent

High gradient - low resistance

Low gradient - high resistance

What are diodes

Semi conductors that only allow current to flow in one direction

What diode emits light and when does it emit light

A light emitting diode and emits light when current passes through it

How does a simple diode work

It has two layers of semiconductor material and each layer is doped with impurity's to give it certain character

How does a diode only allow current to flow in one direction

In toward bias current can flow because there are missing electrons and these gaps in the missing electrons behave like positivity charged electrons. But in reverse bias the electrons and gaps move away from the junction and deplete it so there are no charge carriers move and no current

What is the resistance for a diode when it is in reverse bias

Infinitely high so no current can flow

What is the equation for resistivity

p = RA/L

p = resistivity

R = resistance

L = length

A = area

How do you determine the resistivity of a wire

Plot a graph of resistance against lenght then use the equation of the line y=mx+c and the gradient of the line is equal to p/A so you times it by area to get resistivity

What is resistivity measured in

Ohm metres (Ωm)

What is the temperature called when a superconductor has a resistance of 0

Critical temperature

At what temperature does the Kelvin scale start in degrees Celsius's

-273 ^C

What is a NTC thermistor?

Resistance decreases as temperature goes up (opposite to convention)

What are thermistors made from

Semiconductors

What is a PTC thermistor?

A thermistor that when the temperature increases the resistance also increases

What are themistors used in

Devices where temperature needs to be read or regulated

What does the I-V curve of a NTC thermistor look like

As p.d. Increases the current increases. Which causes the temperature to increase which then decreases the resistance and current then

What will happen if a thermistor exceeds the maximum potential difference

It will burn out because of the rapid increase in current

What does LDR stand for

Light dependent resistor

What is an ldr made from

A semi conductor material

What does the amount/intensity of light change in a ldr

The number of charge carriers

What happens when light shines on a LDR

It's resistance increases drastically

What is intensity proportional to in a ldr

1/d^2

d = distance

What are ldrs partially sensitive to and what does it make them good for

Infrared radiation which makes them particularly useful as sensors in infrared astrology

What is power

Rate transfer of energy

What is power measured in

Watts (W)

What is a watt equal to

Js^-2

What is electrical power

Rate energy transfer of energy by an electrical component or appliance

What is the equation for electrical power

P = VI

an equations for power

P = VI

P = I^2 R

P = (v^2)/R

What is electricity that we consume measured in

kWh

What is a kilowatt hour

The unit equivalent of a 1 kW device being run for an hour