Topic 2 - Controlling And Using Electric Current Flashcards
What is the unit for current?
Amps, A
What is voltage?
The driving force that pushed the current round. Electrical pressure.
What is the unit for voltages
Volts, V
What is resistance?
Anything in the circuit which slows the flow down.
What unit is resistance?
Ohm; Ω
What is potential difference?
Voltage/electrical pressure/energy transferred per unit charge passed.
What happens to charge when it ‘falls’ through a voltage drop?
It gives up energy
How many volts is 1joule/coulomb
1 volt
What happens to current at a junction?
It is conserved. Currents doesn’t get used up or lost in a circuit so current at a junction is conserved. Total current entering a junction is equal to the total current leaving a junction.
What’s the formula for resistance?
Voltage = current x resistance
Describe an experiment you can do to investigate resistant
Set up a standard circuit (with a component voltmeter and ammeter) measure the current and voltage. Ammeter must be placed in series. Voltmeter must be placed in parallel with the component. As you vary the variable resistor it alters current. Record all your readings and plot them on a V-I graph
What type of resistor does this graph represent?
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Fixed resistors
What type of resistor does this graph reprisent?
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Filament lamp
What type of resistor does this graph represent?
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Diode
What type of resistor is this?
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Light-Dependent Resistor (LDR). This is a special type off resistor that changes it’s resistance depending on how much light there is: in bright light resistance falls. In darkness resistance is highest.
What type of resistance is this
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Thermistor (temperature-dependant resistor). Hot - resistance drops Cool - resistance goes up
What is BIRD TURD?
B- Brightness
I- Increase
R- Resistance
D- Decrease
T- Temperature
U- Up
R- Resistance
D- Down
Why do resistors get hot?
Energy transfer when electrons collide with ion lattice that makes up the resistor, energy is released as heat.
What are the negative effects of the heating effect on resistors?
The hearing effect increases the resistors resistance so less current will flow. Causes circuit to be less efficient. Can cause components in the circuit to melt.
What are the positive effects of the heating effect on resistors?
Fuses protect circuits - they melt and break the circuit of the current gets to high Good for heating things (toasters contain a coil of wire wit high resistance. It heats up so much it glows and gives of infrared heat - light bulbs work in a similar way)
What is electrical power?
Rate at which an appliance transfers energy
What is the formula for power?
Power = volts x current
What is the unit for power
Watts, W
What is the formula for energy transferred?
Energy transferred = current x voltage x time
What is current?
The rate of flow of charge round the circuit. Will only flow through a component if there is voltage across that component.