## 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