9 - Energy, power and resistance Flashcards
What are the rules for drawing circuit diagrams?
- Use standard circuit symbols
- No gaps between wires
- Straight lines with pencil and ruler (or careful sketch)
What is polarity?
Whether something is positive or negative.
What does potential difference measure?
The amount of work done per unit charge.
Define 1 volt.
The potential difference when one joule of energy is used to move one coulomb of charge through the component.
What is electromotive force (emf)?
The amount of energy given to each coulomb by the battery.
What is a thermionic emission?
When an object is heated and the electrons gain enough energy to escape from the surface of the metal.
What is a cathode?
A negatively charged electrode.
What is an anode?
A positively charged electrode.
How does an electron gun produce a beam of electrons?
- Metal filament is heated > thermionic emission
- In a vacuum, potential difference is applied to the filament and an anode, causing the electrons to accelerate through a small hole to form a beam.
- Electrons move through a gas which lights up
What does a high resistance mean?
A lot of energy is required to push electrons through a component.
What does Ohm’s law state?
For a metal conductor kept at a constant temperature, the current in the wire is directly proportional to the p.d across the wire.
What happens when the temperature of a metal wire increases and why?
Its resistance increases, which decreases the current because the positive ions gain more energy and vibrate with a greater amplitude which increases the number of collisions between them and the free electrons. This means that more electrons will need to pass through the wire for the same amount to reach the other side, which means that more energy is transferred.
Define the ohm.
The amount of resistance when a potential difference of 1 volt produces a current of 1 amp.
Describe the relationship between voltage and current for an ohmic conductor.
Linear
What is a component that does not follow Ohm’s law called?
A non-ohmic component.
Why are diodes different to other electrical components?
They only allow current to flow in one direction.
Why are LEDs special?
They are made from a material which emits light as it conducts. Electrical energy is transferred directly into light which means that LEDs do not get hot and are extremely efficient.