# Topic 5 Electric Currents

## 18 terms

### ideal ammeter

an instrument used to measure the current flowing in an electric circuit and is always connected in series. An ideal ammeter should have extremely low resistance.

### ampere

defined in terms of the force per unit length between parallel current-carrying conductors.

### conductor

have a low electrical resistance and are therefore able to carry an electric current withour much energy dissipation as heat.

### conventional current

flows from the positive to negative terminal.

### electric current

the rate at which charge flows past a given cross-section.

### electric potential difference

The work done per unit charge to move a small positive charge between the two points.

### electrical resistance

the ratio of the potential difference across the material to the current that flows through it. The units of resistance are volts per ampere (V A^-1). However, a separate SI unit called the ohm Ω is defined as the resistance through which a current of 1 A flows when a potential difference of 1 V is applied.

### electromotive force (emf)

the work per unit charge made available by an electrical source.

### electron flow

flows from the negative to the positive terminal.

### electron-volt (eV)

the energy acquired by an electron as a result of moving through a potential difference of one volt.

### insulator

the electrons are held tightly by the atomic nuclei and are not as free to move through a material. They can accumulate on the surface of the insulator but they are not conducting.

### internal resistance

the resistance inside a source of electrical energy.

### electrical energy

this is energy that is usually associated with an electric current and that is sometimes referred to incorrectly as electricity.

### kilowatt-hour (kWh)

the energy consumed when 1 kW of power is used for one hour.

### Ohm's law

the current is directly proportional to the potential difference at a constant temperature

### ideal voltmeter

is used to measure the voltage drop across part of an electric circuit and is always connected in parallel. An ideal voltmeter has a high amount of resistance.

### NTC thermistor

(negative temperature coefficient) the resistance decreases when the temperature rises and theytherefore pass more current.

### light dependant resistor (LDR)

is a photo-condutive cell whose resistance changes with the intensity of the incident light.