Electricity Flashcards
From which terminal to which terminal do electrons flow?
From the negative terminal to the positive terminal.
What is Kirchoff’s first law?
The sum of the currents entering a point equals the sun of the currents leaving that point.
From which terminal to which terminal does conventional current flow?
From the positive terminal to the negative terminal.
Define electrical resistance.
Potential difference/current - measured in ohms.
A thermistor and a switch are connected in series.
Explain why the current increases when the switch is closed.
When the switch is closed, current flows through the circuit.
Higher current = higher temperature
higher temp of thermistor = lower resistance
lower resistance = increase in current
State ohms law
The current through a device is directly proportional to the potential difference across its two ends.
What would the I-V graph of a metallic conductor look like?
A straight line through the origin. I is directly proportional to V.
What would the I-V graph of a semiconductor look line?
A smooth curve (divergent) starting at the origin.
What would the R-V graph of a metallic conductor look like?
A smooth curve (divergent) starting at the origin.
What is the difference between e.m.f. and p.d.?
E.m.f. is energy transferred into all forms of energy, whereas p.d. is energy transferred into electrical energy only.
Define current
The rate of flow of charge
What does ‘number density’ mean? Give the unit
The number density of charge carriers is a property of a material that shows how many electrons that pass through the material per m3. Unit: m-3
Define the coulomb.
When a current of 1A flows for 1s, 1C of charge is said to be passed.
What four factors does the resistance depend on?
1) Material
2) Length
3) Cross-sectional area
4) Temperature
Define the ohm
A device has a resistance of 1 ohm if a current of 1A flows through it when a p.d. of 1V is applied across its end.
