# AQA A GCE Physics - Current Electricity

- Created by: Quincy Washington
- Created on: 02-12-10 18:10

What is current?

**-Rate of flow of charge**

How can you calculate current using time?

**-****Δ****Q/****Δ****t**

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…

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