Electrical circuits Flashcards
what is electrical current?
the flow of electric charge around the circuit
when will current only flowaround a circiut?
a current will only flow around a complete (closed circit if theres a potential difference.
what is the unit for current?
ampere A
what is potential difference (voltage)?
the driving force that pushes the charge around
what is the unit for potential difference?
volt V
what is resistance?
anything in the circiut that slows the flow down
what is the unit for resistance?
ohm 0
what does the current flowing through a component depend on?
the potential difference across the component and the resistance of the component
the greater the resistance accross a component…..
the smaller the current that flows through it (for a given potential difference accross the component
what is the equation that links charge, current and time?
Q=IxT
more charge passes around a circiut when……
a bigger current flows
what is the formula for potential difference and resistance?
v = IxR
does the resistance of ohmic conductors change the current?
no
at a constant temperature the current flowing through an ohmic conductor is …………
directly proportional to the potential difference accross it.
what is an example of resistor or component that doesnt change its resistance
a filament lamp or a diode
how does a filiment lamps resistance work?
when the electrical charge flows through a filiment lamp it transferes some energy to the thermal energy store of the lamp, which is designed to heat up. resistance increases with temp so as the current increases, the resistnace increases.
how does a diode resistance work?
the resistnace depends on the direction of the current, they will hapily let current flow in one direction, but have a very high resistance if its reversed.
when your investigating where must the ammeter always be placed?
in series with whatever your investigating
when your investigating where must the voltmeter always be placed?
in parralel with whatever your investigating
what is the method for the required practical ‘investigating resistance’?
1) attach a crocodile clip to the wire level with 0cm on the rule
2) to attach the second crocodile clip to The Wire 10 cm away from the first clip between the clips
3) close the switch then record the current through the wire and the potential difference across it
4) Open the switch then move the crocodile clip another 10 cm along the wire closer switch again then record the new length current and potential difference
5) repeat this for a number of different lengths of the test wire
6) use your measurements of current and potential difference to calculate the resistance of each wire using V=Ixr
7) Plot a graph of resistance against the wire and draw a line of best fit
8) Your graph should be a straight line through the origin meaning of resistance is directly proportional to length, the longer the wire the greater the resistance
9) if your graph doesn’t go through the origin it could be because the first clip isn’t attached exactly 0 cm so all of the length readings are a bit out, this is a systematic error
what are some factors resistance can depend on?
wheather the circiut is in series or parralel or the length of a wire
what does the term IV characteristic mean?
a graph which shows how the current flowing through the component changes as the potential difference across it has increased
what does the IV characteristic for linear components look like?
a straight line
what does the IV characteristic for a non- linear components look like?
a curved line
what is the method for the required prcatical IV chatacteristics?
1) Set up the test circuit With a variable resistor battery voltmeter ammeter and component.
2) Begin to vary the variable resistor. this alters the current flowing through the circuit and the potential difference across the component.
3) take several pairs of readings from the ammeter and voltmeter to see how the potential difference across the component varies as the current changes. repeat each reading twice to get more of an average potential difference at each current
4) Swap over the wires connected to the battery to the direction of the current is reversed
5) plot a graph of current against voltage of the component
how should the graph for an ohmic conductor look like?
the current through an ohmic conductor at a constat temp is directly proportional to a potential diffference, so you get a staight line.
how should the graph for a filiment lamp look like?
as the current increases, the temperature of the filiment lamp increases, so the resistance increases. this means less current can flow per unit of potential difference, so the graph gets shallower - hence the curve
how should the graph for a diode look like?
current will only flow through a diode in one direction. the diode has a very high resistance in reverse direction.
