P2 (Electricity) Flashcards
What is electric current?
The flow of electrical charge.
What is the equation for electrical charge?
Q=It
Charge = current x time
charge (coulombs), current (amperes), time (seconds)
What is the value of current at any point in a series circuit?
Current is the same at all points in a series circuit.
What two factors does the current in a circuit depend on?
Potential difference, resistance.
What is the equation for potential difference?
V=IR
Potential difference = current x resistance
potential difference (V), current (A), resistance (Ω)
What is an Ohmic conductor?
- A conductor for which current and potential difference and directly proportional.
- Resistance remains constant as current changes.
- Temperature must be constant.
What are four components for which resistance is not constant as current changes?
Lamps, diodes, thermistors, light dependent resistors (LDR).
What happens to the resistance of a filament lamps as the temperature increases?
- Resistance increases.
- Ions in metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow.
Describe the current flow in a diode?
- The current only flows in one direction.
- Resistance is very high in the other direction, preventing current flow.
What happens to resistance of a thermistor as temperature increases?
The thermistors resistance increases.
When might a thermistor be used?
- In a thermostat to turn a heater on below a certain temperature.
- In a freezer to turn on a cooler when the temperature becomes too high.
What happens to the resistance of a LDR as light intensity decreases?
The LDR’s resistance increases.
When might an LDR be used?
- Street lights often use LDRs.
- When light levels become too low, the light gains sufficient current to turn on.
What is a series circuit?
Series circuit is one loop; all electrons in that loop form one current.
What is a parallel circuit?
In a parallel circuit, electrical components are connected along side one another, forming extra loops.
Describe the potential difference in a series circuit?
Potential difference is shared between each component.
Describe the potential difference in a parallel circuit?
Potential difference across each component is the same.
Describe the resistance in a parallel circuit?
The total resistance is less than the smallest of the two individual resistance.
Describe the resistance in a series circuit?
The total combined resistance is equal to the sum of the two individual resistances.
Describe the current in a series circuit?
In a series circuit, the current is the same e at all positions since the charge only has one path to flow through.
Describe the current in a parallel circuit?
In a parallel circuit, the current is shared between the different branches. When the charge reaches a junction, it splits.
How should you connect an ammeter in a circuit to measure current?
Ammeters should be connected with component that they are measuring current through.
How should voltmeters be connected in a circuit?
Voltmeters should be connected in parallel to the component that they are measuring the potential difference of.
Why is it better to connect lamps in parallel?
If one lap blows, the rest will be unaffected and can still receive current (i.e the circuit is still complete)
