Flashcards in Topic 2 - Controlling and Using Electric Current Deck (32):
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?
What is voltage?
Potential difference, driving force that pushes current around, like electrical pressure
What is the unit to measure voltage?
What is resistance?
Anything in the circuit which slows the flow down
What is resistance measured in?
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?
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?
What is 1 volt in joules/coulombs?
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?
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?
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
-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?
What is the equation linking electrical power potential difference and current?
Electrical power = potential difference x current