Electricity: Energy, Power and Resistance Flashcards
What is the electromotive force (e.m.f) of a supply?
The energy gained per unit charge by charges passing through the supply. Measured in volts (V)
What is potential difference?
The energy transferred per unit charge by the charges passing through a component.
What does Ohm’s law state?
The current through a conductor is directly proportional to the potential difference across it, provided that physical conditions like temperature remain constant.
What is resistance?
A property of a component that regulates the electric current through it in ohms.
What factors affect electrical resistance?
- Material the wire is made of
- Length of the wire
- Cross-sectional area of the wire
- Temperature of the wire
How does the material a wire is made from, affect its electrical resistance?
Insulators such as plastics do not have free electrons whereas metals have free electrons and so can carry charge.
How does the length of a wire, affect its electrical resistance?
As the length of a conductor increases, so does its electrical resistance because the electrons experience a smaller potential gradient as the wire gets longer.
How does the cross-sectional area of a wire, affect its electrical resistance?
Resistance is inversely proportional to the cross-sectional area of a wire. This is because there is a bigger volume of electrons available to flow at the same drift velocity.
How does the temperature of a wire, affect its electrical resistance?
As the temperature of a wire increases, the resistance increases. This is because the particles have more vibrational kinetic energy and will better resist the flow of charged particles.
What is the IV characteristic of a resistor?
Current is directly proportional to the potential difference.
What is the IV characteristic of a filament lamp?
At low temperatures it follows Ohm’s law but as the current increases, the electrons more more quickly leading to more collisions, giving them more KE and therefore a greater temperature, so current increases slower than PD.
What is the IV characteristic of a diode/LED?
No current can and the diode has near infinite resistance in the reverse bias direction and the current will flow through the forward bias direction.
What is a kilowatt-hour?
3,600,000 J. It is used for paying energy bills as it makes the numbers more manageable.
