# Electricity And Magnetism

- Created by: tiny-turntable
- Created on: 15-10-15 07:49

## Identify two types of electric charge

There are two types of charges:

Positive charges – indicated as (+)

Negative charges – indicated as (-)

Electric charges are carried by particles.

Protons are positive particles

Electrons are negative particles

## Apply law of conservation of charge

Electric charge (electrons) cannot be created nor destroyed, only moved.

When an atom donates an electron to react they do not disappear, they always go somewhere else.

It is important to remember that the number of positive charges is always equal to the number of negative charges in nature.

When a material has a charge that is not neutral, we describe the material by the relative balance of particles present… more electrons = negative more protons = positive

As mentioned earlier, nature exists in a neutral balance, so a positive will draw electrons toward and a negative will move electrons away from.

## Difference between conductors and insulators

Describe and explain the difference between conductors and insulators.

Conductors and insulators are best described as opposites of each other.

Conductor

Electricity is about moving electrons, so a conductor is any material that will allow electrons to move through it easily.

A conductor transmits electricity easily --> due to the loose valance electrons of the atoms in the material --> which means that the electrons can easily be affected and moved --> A kind of domino effect is created.

Insulator

An insulator is any material that will not allow electrons to move through easily.

An insulator does not transmit electricity easily --> as the valance electrons are held tight, close to the nucleus --> which means that the electrons are not easily affected or moved

## Concept of electric field and charge behaviour

Describe the concept of electric field and how charges behave in electric fields.

An electric field is formed by charged particles.

Electric fields exist in the area around a charged particle. The field can be seen as lines going into or out of the particle.

A positive particle has field lines moving away from the particle and a negative particle has field lines moving into the particle.

## Coulomb’s Law

State Coulomb’s Law and solve basic problems based on it.

The force that causes charged particles to be attracted or repelled can be described mathematically using Coulomb’s Law. Coulomb’s Law relates the electrical charge and the distance between the charges to describe the electrical force.

The formula for the electrical force between charged particles is:

F is the electrical force between the particles (it is measured in Newtons (N)). If it is positive (+) it is repulsive, if it is negative (-) it is attractive

k is called Coulomb’s constant. It is always the same value, we will call it 9 (in reality it has a value of 9 x 10^{9} (no units)).

q_{1} and q_{2}are the charges on the particles (measured in Coulombs (C)). They can be positive (+) or negative(-).

D is the distance between the particles (measured in meters (m)). It is always squared in the equation.

## The symbols used in circuit diagrams

Identify and properly use the symbols used in circuit diagrams: cell, battery, wire, bulb, ammeter, voltmeter, resistor.

## Calculate the equivalent R for simple combinations

Series

Parallel

When you have the fraction for the Rs added together you flip it to get Rtotal

## The differences between series and parallel circui

Draw and identify the differences between series and parallel circuits.

Series

1 branch only, **current** is the **same** all over circuit, **voltage** is **shared**, divided.

Parallel

2+ branches, **current** is **shared**, divided, **voltage** is the **same** all over circuit.

## How a voltmeter/ammeter should be connected

State and explain how a voltmeter/ammeter should be connected

Voltmeter

Connected in parallel around each resistor.

Ammeter

Connected in series at the beginning and end of the circuit and if the circuit is parallel at the start of the different branches too.

## The concept of Q, I, V and R + P

Explain using the correct units the concept of charge, current, potential difference and resistance

Voltage (V) = potential difference. Potential Difference is the energy used to move a charge. It is measured in volts (v). Symbol for Potential Difference is V.

Current is the charge passing through the circuit over time. It is measured in Amperes or Amps (A). Symbol for current is I.

Power (P) - watt (W). Electric Power is how much work the circuit is doing.

Charge (Q) - Coulomb (C). The capacity of the battery to maintain a current over time.

## Conventional current and electron flow

Distinguish between conventional current (+ to -) and electron flow (- to +)

## Length and thickness of wires: related to resistan

Explain how the length and thickness of wires is related to their resistance.

Resistance is how much the flow of electrons is slowed in the circuit. Symbol R. Resistance is measured in Ohms (Ω) and is related to four conditions:

Type of material: Good conductors like silver have less resistance than lead.

Length of the circuit: The longer the circuit, the greater the resistance.

Cross-sectional area of the wire: Thick wire will have less resistance than thin wire.

Temperature: The higher the temperature, the greater the resistance. This is why computers have fans to cool them.

## Ohm’s Law

Describe Ohm’s Law and apply it to calculate quantities in Ohmic resistors in simple series and parallel circuits.

Ohm’s Law expresses the relationship between resistance, current and potential difference. It is expressed mathematically as V = IR.

Electric Power is how much work the circuit is doing. The unit of Electric Power is Watts (W). We express Electric Power mathematically as P = IV

## Resistivity

Explain the concept of resistivity (as opposed to resistance) and compare different conducting materials.

A measure of the resisting power of a specified material to the flow of an electric current.

## Magnetic Poles

State the two types of magnetic poles, and that they are always found in pairs.

Identify the formation of magnetic field lines due to like and/or opposite poles.

North & South - always found in pairs because of domains

## Direction of magnetic fields

Determine the direction of magnetic fields (using right hand rule)

due to electric currents on current-carrying wires (straight or coiled)

## Electric & magnetic fields

List the similarities and differences between electric and magnetic fields

**Similarities**:

- Always moves from one side to the other
- Same sides repel
- Opposite sides attract

**Differences**:

- Moves from North to South/Negative to positive
- Domains/Charged atoms
- Works at distance (mag.)/ requires contact (el.)

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