electricity Flashcards
what is current?
the rate of flow of charge
definition of a coulomb
the amount of charge that passes in 1 second when the current is 1A
what measures current through a circuit?
ammeter
where would you attach an ammeter in a circuit?
always in series
what is potential difference between two points?
the work done in moving a unit charge between two points
what measures pd in a circuit?
voltmetre
where do you attach a voltmeter to measure pd?
across the component in parallel
how do you draw a fuse on a circuit diagram?
rectangle with line going straight through it in horizontal direction
how do you draw a thermistor on a circuit diagram?
draw a resistor then horizontal line directly under start of rectangle, turned 45 degrees into a horizontal line through rectangle like variable resistor
how do you draw a diode on a circuit diagram?
horizontal line, draw a circle with line going through centre, draw a triangle with a line at the narrowest part inside circle
how to draw an LED on a circuit diagram
diode but with two arrows pointing north east from circle
how to draw a LDR (light dependant resistor) on a circuit diagram?
resistor with a circle around the rectangle and two arrows pointing south east into the circle
what is power?
the rate of transfer of energy
measured in Watts
what are the four equations for power?
power=energy (J) / time
power= current x pd
power= pd squared/ resistance
power= current squared x resistance
what are the three equations for total electrical energy transferred?
E= I x t x V
E= (pd squared/ resistance) x t
E= current squared x resistance x t
what is internal resistance
in a battery, chemical energy is used to make electrons move
as they move they collide with atoms inside the battery so they will have some resistance called internal resistance
what is load/ external resistance?
the total resistance of all the components in a circuit
what is emf?
electromotive force
the amount of electrical energy the battery produces and transfers to each coulomb of charge
measured in volts
what is terminal potential difference?
the energy transferred when one coulomb of charge flows through a resistor
with no internal resistance its the same as emf
what are lost volts?
the energy wasted per coulomb overcoming internal resistance
how can you measure internal resistance and emf of a cell or battery? RP6
set up circuit- battery in series with ammeter and voltmeter. variable resistor in parallel with switch.
- set the variable resistor to the highest resistance
- close the switch and record the current and pd
- open the switch and close it again 2 more times to calculate mean current and pd
- decrease the resistance of the variable resistor and then repeat previous steps with this resistance
- keep decreasing the resistance till you have 10 readings
- plot a V-I graph for mean data and draw line of best fit
is charge conserved in a circuit?
yes
what’s Kirchhoff’s first law?
current entering a junction = current exiting the junction