# AQA A GCE Physics - Current Electricity

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What is current?

-Rate of flow of charge

How can you calculate current using time?

-ΔQ/Δt

What is ΔQ measured in?
-Coulombs (unit of charge)

Define 1 Coulomb

-Amount of charge that passes in 1 second when the current is 1 ampere

How can you measure current flowing through a circuit?

-Ammeter

Where does an ammeter need to be attached in a circuit? Why?

-Series

-Current through ammeter is the same as current through the component

Define potential difference

-Energy converted per unit charge moved

What needs to be done to electric charge to make it flow through a conductor?

-Work must be done on it

How can you work out voltage using charge?

-W/Q

What is ‘W’ in order to work out potential difference?
-Energy in joules, work done to move the charge

Define a volt

-Potential difference across a component is 1 volt when you convert 1 joule of energy moving 1 coulomb of charge through the component

Finish this equation in terms of the definition of potential difference.

-1V = 1JC-1

What does current for a particular potential difference depend on?

-Resistance of component

How do you calculate resistance using voltage?

-V/I

What is resistance measured in?

-Ohms (Ω)

A component has a resistance of 1 Ω if a potential difference of 1 V makes a current of *A flow through it

-1A

For what sort of conductor is resistance a constant?

-Ohmic conductor

What sorts of conductors obey Ohm’s law?

-Ohmic conductor

Name 2 factors that are directly proportional in an Ohmic conductor. What must remain constant?

-Current and potential difference

-Temperature

How will factors such as light level or temperature have significant effects on resistance?

-Resistivity changes

Finish this sentence: “Ohm’s law is a special case; it is only true for…

-Ohmic conductors at constant temperature

What do I/V graphs/characteristics show?

-How resistance varies

What does the gradient of an I/V graph show?

-Resistance. Shallower the gradient of a characteristic I/V graph, the greater the resistance of the component

What is the I/V characteristic for a metallic conductor?

-Straight line through zero (0)

Which I/V characteristic is a curve through zero (0)?

-I/V characteristic for a filament lamp

Why doesn’t a filament lamp have the same (straight line) characteristic of a metallic conductor?

-Gets hot. Current flowing through lamp increases its temperature

The ********** of a metal increases as the temperature increases

-Resistance

Where are semiconductors used?

-Sensors

Describe semiconductors

-Nowhere near as good at conducting as metals, due to few charge carriers. If energy is supplied to semi-conductor, more charge carriers can be released. Meaning they make excellent sensors for detecting changes in their environment

Which 3 semiconductor components do you need to know about?

-Thermistors, LDRs (Light Dependent Resistors), Diodes

What does resistance of