Required practical 4 - Current and p.d characteristics Flashcards
What does this practical aim to investigate
how the current through a component depends on the pd of the component
How do we do this practical with a resistor
- Set up a circuit containing a battery, wire, a resistor in series with a variable resistor and ammeter and a voltmeter in parallel
- use the voltmeter to read pd across the resistor
- use the ammeter to read current across the resistor
- Adjust the variable resistor and record the new readings on the voltmeter and ammeter
- Switch the direction of the battery
- Both the voltmeter and ammeter should have negative values
- Continue taking several readings of pd and current
How should a ohmic conductor graph look like
a straight line through zero, meaning the current through a resistor is directly proportional to the pd
why should you not leave the circuit connected for too long
the temperature of the resistor might increase
what difference do we get when we do this experiment with a filament lamp
the current in a filament lamp is not directly proportional to the pd, this is because, when current increases, the temperature of the lamp also increases, and the increased temperature causes resistance to increase
why are extra resistors added in this experiment when we use diodes
because diodes are very easily damaged by high currents, the extra resistor will keep the current relatively low and protect the diode
what type of ammeter do we use in a circuit with a diode
milliammeter
what type of results do we get when doing this experiment with a diode
- we only get a current when pd is around 0.6 - 0.7 V, as pd rises above this point, current increases sharply
how do we change the practical when using a diode
we add an extra resistor in series as diodes are very easily damaged by high currents, so the extra resistors will keep current relatively low and protect the diode
