# Physics P3: Electricity

by Phillip CONRAD
# 1. Potential Difference and Electromotive Force

## 1.1. Potential difference is a measure of energy in each charge flowing in a wire.

## 1.2. Potential difference is measured in volts, and measured by a voltmeter.

### 1.2.1. Voltage is equal to the energy (in joules) divided by the charge (in coulombs)

### 1.2.2. Voltmeters are always connected in paralell

## 1.3. Electromotive force (EMF) is another term that is used to denote a voltage. EMF is used to describe the energy per unit charge driving current around a circuit, whereas a potential difference is the energy per unit charge diving current between any two points in a circuit.

# 2. Static Electricity

## 2.1. Electrons captured carry negative charge, so an object that is negatively charged has an excess of electrons, while an object that is positively charged has a shortage of electrons.

## 2.2. Like charges repel each other, while unlike charges attract each other.

## 2.3. An electric field is a region where an electric charge feels a force.

## 2.4. Objects can be charged by rubbing. This is not due to the creation of electrons, but the transferral of electrons from one material to another.

## 2.5. Charge is a property of matter.

# 3. Current Electricity

## 3.1. Current electricity is the flow of electrons along a wire.

## 3.2. Measure of charge is the coulomb, (C) and it is defined in terms of the ampere.

### 3.2.1. Q=IxT

3.2.1.1. Charge is equal to current times time.

### 3.2.2. The charge of Six times 10^18 electrons equals one coulomb

## 3.3. The unit of current is an ampere (A), which is measured by an ammeter.

# 4. Resistance

## 4.1. The larger the resistance, the smaller the current.

## 4.2. Measured in Ohms, and measured by the Greek Omega letter. Ranges from 0.1 Ohms, to billions of ohms.

## 4.3. Voltage is equal to the current multiplied the resistance.

# 5. Electrical Power

## 5.1. Power is measured in watts, or also joules per second.

## 5.2. Power is equal to the current multiplied by the voltage.

# 6. Misc.

## 6.1. Energy (in joules) is equal to the voltage, current, and time all multiplied.

## 6.2. Energy can be thought of as power multiplied by time.

# 7. Laws

## 7.1. Charge (in Coulombs) is equal to the current (in amperes) times time (in seconds).

## 7.2. Potential Difference (in volts) is equal to the energy (joules) over charge (in coulombs).

## 7.3. Potential Difference (In volts) is equal to the current (in amperes) multiplied by the resistance (in ohms).

## 7.4. Energy (in joules) is equal to the potential difference multiplied by the current (in amperes) and the time (in seconds).

## 7.5. Power output (in watts) is equal to the current (in amperes) multiplied by the potential difference (in volts).

## 7.6. Power output (in watts) is equal to the energy (in joules) transferred over time taken (in seconds).

# 8. Units

## 8.1. Ampere (I) Current

## 8.2. Coulomb (Q) Charge

## 8.3. Time (t) Seconds

## 8.4. Voltage (V) Potential Difference

## 8.5. Energy (E) Joules

## 8.6. Ohms (Greek symbol) Resistance

## 8.7. Watts (W) Power Output