resistors

what does the resistance tell us

the potential difference required to drive a current through a component / or how much energy is required to push a coulomb of charge through

what is the unit for resistance

ohms

at a constant temperature, describe the relationship between current and potential difference through a ohmic conductor

The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor. This means that the resistance remains constant as the current changes. This means graph will show a straight line passing through zero

what is an ohmic conductor

A conductor that obeys Ohm's Law i

graph showing resistance of filament lamp

how does the resistance of a filament change

The resistance of a filament lamp increases as the temperature of the filament increases. Because at higher temp, atoms in filament vibrate more and so the electrons in the current collide more with the atoms and so more energy needed to push the current through the filament -the graph shows this as the potential difference increases, the current no longer increases as much

current-potential difference graph for a diode

-will not let any current flow on the opposite direction because high resistance

LED

gives off light when a current flows trough

-are extremely energy-efficient source of light

required practical 4: describe how to investigate the current/voltage characteristics of circuit components-resistor

-get a battery connected by wires to a resistor. The resistor is in series with an ammeter and a variable resistor. We have a voltmeter in parallel across the resistor

1. use the voltmeter to read pd across the resistor

2. use ammeter to read current through the resistor

3. record these values

4. adjust the variable resistor and record new readings on the voltmeter and ammeter

5. need to do this several times to get a range of readings

6. switch the direction of the battery, which will mean that the direction of the pd has now reversed -the ammeter and voltmeter will give negative values

7. plot a graph of the current against the pd -for resistor will be a straight line going through zero telling use that the current through the resistor is directly proportional to the pd-we will only see this if the temperature is kept constant and so important not too leave the circuit connected for too long

equired practical 4: describe how to investigate the current/voltage characteristics of circuit components-filament lamp

-just like before, adjust the variable resistor and read both the pd and the current and we do this for a range of values with the battery in the forward and reverse direction

-the graph will show that the current is not proportional to the pd because when current increases the temp of filament lamp increases and so resistance increase

quired practical 4: describe how to investigate the current/voltage characteristics of circuit components-diode

circuit will have an extra resistor because diodes are very easily damaged by a high current and so the extra resistor keep the current relatively low and protect the diode

-becuase the current will be low, need a very sensitive ammeter -milliammeter

-again we adjust the variable resistor a number of times and record the pd and current