2.1 - Current, Potential Difference and Resistance Flashcards
What is required for electrical charge to flow through a closed circuit?
The circuit must include a source of potential difference.
What is electric current?
Electric current is a flow of electrical charge.
What does the size of an electric current mean?
The rate of flow of electrical charge (how fast the charge is flowing)
How are Charge flow, current and time linked?
Charge Flow = current × time
[Q = I × t]
What is the unit for Charge?
Coulomb ( C )
What symbol is normally used to represent charge in equations?
Q
What is the unit of current
Amperes ( A )
What is the symbol normally used to represent current in equations?
I
How does current change around a closed loop?
It doesn’t: a current has the same value at any point in a single closed loop.
What is the symbol for an open switch?
What is the symbol for a closed switch?
What is the symbol for a lamp?
What is the symbol for a fuse?
What is the symbol for a cell?
What is the symbol for a voltmeter?
What is the symbol for a battery?
What is the symbol for an ammeter?
What is the symbol for a diode?
What is the symbol for a thermistor?
What is the symbol for a resistor?
What is the symbol for a variable resistor?
What is the symbol for an LDR?
What is the symbol for an LED?
What two properties of a component affect the current passing through it?
Resistance of the component and potential difference across it
How are current, resistance and potential difference related for a component?
potential difference = current × resistance
[V = I R]
What is the unit of potential difference?
Volts ( V )
What is the symbol normally used to represent potential difference in equations?
V
What is the unit of resistance?
Ohms ( Ω )
What is the symbol normally used to represent resistance in equations?
R
In what conditions the current passing through a component directly proportional to the potential difference across it?
- If the component is ohmic
- If the component is at constant temperature
What is an ohmic conductor
A component for which the resistance stays constant for a given current and potential difference.
(A component that obeys Ohm’s law [V = IR])
How are current and potential difference related for ohmic components?
Resistance is constant, so current is directly proportional to potential difference (V = IR)
Do all components have a fixed resistance?
No, the resistance of components such as lamps, diodes, thermistors and LDRs is not constant; it changes with the current through the component.
How does the potential difference of a filament lamp change as current increases
- Current increase leads to temperature increase (light turns on)
- Temperature increase leads to resistance increase
- Resistance increase leads to potential difference decrease (V = IR)
How does the potential difference of a diode change as current varies?
- Diode only let current flow in one direction
- When current is negative, resistance is very high
- Very high resistance, so potential difference is very low (V=IR)
- When current is positive, resistance is very low
- Very low resistance, so potential difference is very high (V=IR)
What is a thermistor?
A component where the resistance decreases as the temperature increases
What might a thermistor be useful for?
Electrical circuits which need to vary based on temperature (e.g. a thermostat)
What is an LDR
Light Dependent Resistor
Resistance decreases as light intensity increases
What might an LDR be useful for?
Electrical circuits which need to vary based on light (e.g. streetlamps which turn on when it gets dark)
How can you measure the resistance of a component?
- Create a circuit with the component
- unbroken circuit
- has a power source
- Measure the current passing through the component
- Ammeter
- In series (current is the same for components in series)
- Measure the potential difference passing through the component
- Voltmeter
- In parallel (potential difference is the same for components in parallel)
- Resistance is the potential difference divided by the current (V = I R )
