Electricity Flashcards
What’s the unit for current?
A
Amps
What’s the unit for voltage?
V
Volts
What’s the unit for resistance?
Ω
Ohms
What’s the unit for power?
W
Watts
What’s the unit for charge
C
Coulombs
What’s the unit for energy
J
Joules
Explain *in terms of electron flow *what is meant by alternating current.
The direction that the electrons flow changes continuously back and forth
What equation do you use to work out the total resistance of the resistors arranged like this in a circuit? Use the relationship sheet to check
_____R1_____R2_____
Total resistance, RT=R1+R2
What equation do you use to work out the total resistance of the resistors arranged like this in a circuit? Use the relationship sheet to check
|___R1____|
|___R2____|
1/RT = 1/R1+ 1/R2
don’t forget to do 1/ [ANS] on calculator at the end to find RT
What is the difference between
DC (direct current)
and
AC (alternating current)?
In DC the current always travels in the same direction.
In AC the current constantly switches direction back and forth
If Voltage stays the same but current increases what must happen to resistance?
Resistance decreases
because V=IR so if I goes up then R must come down
If 2 resistors of different values are arranged in parallel what is the same for each resistor?
Current through the resistor
or
voltage across the resistor?
Voltage across each resistor is the same
current will depend on size of the 2 resistors (bigger R smaller I)
If 2 resistors of different values are arranged in series what is the same for each resistor?
Current through the resistor
or
Voltage across the resistor?
Current is the same through each resistor
Voltage will depend on the size of the resistors - bigger R bigger V
What is unique about a diode?
It only lets current flow in one direction (the direction of the arrow)
When does an LED light up?
When the current is flowing in the direction of the arrow.
An LED doesn’t let current flow in the other direction
If you increase the temperature of a thermistor what happens to the resistance?
Does it go up or down?
Resistance goes down
Remember TURD (Temperature Up, Resistance Down)
If you increase the light on a light dependent resistor (LDR) what happens to the resistance?
Does it increase or decrease?
It decreases
LURD (Light Up,Resistance Down)
If you decrease the temperature of a thermistor what happens to the resistance?
Does it increase or decrease?
Increases
Remember TURD Temp Up Resistance Down or vice versa
If a charged particle is in an electric field what happens to it?
It experiences a force
- A charge will be attracted to a plate of the opposite charge and move towards the plate
- A charge will be repelled by a plate which is the same charge and will move away from the plate
What is meant by potential difference?
Potential difference (or voltage) is the measure of the energy given to the charge carriers in the circuit
In a lamp what happens to the resistance when the lamp turns on?
Resistance increases
It gets hot so the molecules in the lamp move around more
So it’s harder for the electrons to get through - so resistance increases
When does a transistor ‘turn on’
(conduct electricity)
When the input voltage (from ‘base’ to earth) is bigger than the threshold voltage
- NPN transistor (0.7 V)
- MOSFET (2 V)
If you add an extra resistor in parallel what happens to the overall resistance?
Overall resistance goes down
What is the symbol on the formula sheet for current?
I
What is the symbol on the formula sheet for voltage?
V
What is the symbol on the formula sheet for resistance?
R
What is the symbol on the formula sheet for charge?
Q
What is the symbol on the formula sheet for power?
P
What is the symbol on the formula sheet for energy?
E
