Topic 2 - Controlling and Using Electric Current Flashcards
What is current?
Rate of flow of charge around a circuit
What does there need to be in a circuit in order for a current to flow?
A voltage across the circuit
What is the unit to measure current?
Ampere, A
What is voltage?
Potential difference, driving force that pushes current around, like electrical pressure
What is the unit to measure voltage?
Volt, V
What is resistance?
Anything in the circuit which slows the flow down
What is resistance measured in?
Ohm, Ω
What happens to current if you increase the voltage?
More current will flow
What happens to current if you increase the resistance?
Less current will flow
Potential difference is ______ transferred per ____ ______.
Potential difference is energy transferred per unit charge
In a circuit, where is the energy supplied to the charge and how does this affect the voltage?
- Power source
- Increases it
What causes charge to decrease in a circuit?
When voltage decreases my components in the circuit e.g. resistors
If the change in voltage is bigger, how does this affect the amount of energy transferred for a given charge passing through the circuit?
More energy
What is 1 volt in joules/coulombs?
1
How does current change around a circuit?
It doesn’t, current is conserved; the total current entering a junction id = to total current leaving a junction
What does an ammeter measure?
The current flowing through the component in amps
How should an ammeter be put into the circuit?
In series
What does a voltmeter measure?
Voltage/potential difference across the component in volts
How should a voltmeter be placed in a circuit?
In parallel around the component under test
What is the effect of a variable resistor on the current?
Alters the current flowing through the circuit which can be recorded by ammeter/voltmeter, plot on voltage-current graphs
How does a diode affect current?
Current only flows through a diode in one direction
How does a filament lamp affect current?
As temp increases, resistance increases
What si the relation between current through a resistor and voltage?
Propotional
What is the equation linking voltage, current and resistance?
Potential difference = current x resistance
How does an LDR affect resistance?
- Light dependent resistor
- Amount of resistance depends on how light it is
- In bright light, resistance falls
- In darkness, resistance higher
How does a thermistor affect resistance?
- Temperature dependent resistor
- Hot: resistance drops
- Cold: resistance increases
Why do resistors get hot when an electric current passes through them?
- Energy transfer heats resistor
- Energy transfer due to electrons colliding w/ ions in lattice that make up resistor as move through it
- Collisions give ions in lattice extra energy emitted as heat increasing resistor’s resistance reducing curent flow (or more voltage for same current); if too hot, no current flows
- Heating causes circuits to be less efficient as energy wasted. Can cause components to melt (circuit stops working)
- Fuses use this effect to protect circuits: melt + break circuit if current gets too high
What are the advantages of the heating effect in a resistor?
- Good if you want to heat something
- e.g. toasters
- Current passes through coil, temp. increases so much so it glows + gives off infrared (heat) radiation that cooks bread
- Light bulbs work in similar way
How does an appliance with a high power rating transfer energy?
Transfers lots of energy in a short time
What is power measured in?
Watts, W
What is the equation linking electrical power potential difference and current?
Electrical power = potential difference x current
What is the equation linking energy transferred, current, potential difference and time?
Energy transferred = current x potential difference x time
