Required Practicals - Current / PD Flashcards
What is the investigation of the current/pd practical?
To investigate the current/voltage characteristics of circuit components.
What is the circuit for investigating I/V characteristics of a resistor?
A battery, ammeter, variable resistor and resistor in series with a voltmeter in parallel across the resistor.
How do we investigate I/V characteristics of a resistor?
Use the voltmeter to read the p.d. across the resistor.
Use the ammeter to read the current through the resistor.
Record values in a table.
Adjust the variable resistor and record new readings on the voltmeter and ammeter.
Repeat several times to get a range of readings.
Switch the direction of the battery, so the p.d. direction reverses.
The voltmeter and ammeter should have negative values.
Takes several readings again.
Now plot a graph of current against p.d.
What is the graph of the I.V characteristics of a resistor?
The straight line passes through the origin with a constant gradient so is directly proportional for positive and negative values.
Therefore it is an ohmic conductor.
Which condition needs to be maintained to a achieve a directly proportional graph for I.V characteristics of a resistor?
Temperature needs to be constant.
How do we prevent temperature increase during the I.V characteristics practical?
Don’t leave the circuit on for too long.
What apparatus do we use for measuring a filament lamp’s I.V characteristics?
Battery, ammeter, variable resistor and filament lamp in series with a voltmeter in parallel across the filament lamp.
How do we get results for the I.V characteristics of a filament lamp?
Adjust the variable resistor and record ammeter anf voltmeter values.
Reverse the direction of the battery.
Repeat for both directions of the battery.
What is the graph for I.V characteristics of a filament lamp like?
Current is not proportional to potential difference.
Why is current not directly proportional to potential difference in a filament lamp?
As current increases, the temperature increases and this increased temperature causes an increase in resistance.
What is circuit for measuring the I.V characteristics of a diode?
A battery, variable resistor, ammeter, resistor and diode in series with a voltmeter in parallel.
Why is an extra resistor added to the apparatus of measuring I.V characteristics of a diode?
Diodes are very easily damaged by a high current.
The extra resistor will keep the current relatively low and protect the diode.
Why is a very sensitive ammeter needed in the I.V characteristics practical for the diode?
Current will be very low due to the extra resistor, so very small changes in current need to be measured.
What is another name for a very sensitive ammeter?
A milliammeter.
What do we do to find the I.V characteristics of a diode?
Adjust the variable resistor a number of times and record the p.d. and current.
Do this with the battery for the forward and reverse directions.
