Measuring the Resistance of a Component

Question 1

what is the simplest way of setting up a circuit to measure the resistance of a component

Answer 1

• place an ammeter in series beyond the component

- and place a voltmeter in parallel to the component

Question 2

why should you set up a circuit like this

Answer 2

• so that you can measure the current in the resistor

- and the potential difference across it, or the pd it consumes

Question 3

how would you use this information to calculate its resistance

Answer 3

use R = V / I

Question 4

why isnt the reading on the ammeter for the current in the resistor not as accurate as it could be

Answer 4

• because the voltmeter takes up some current in order to operate
• so the reading on the ammeter is less than the actual value the resistor takes up

Question 5

why can this generally be ignored however

Answer 5

• because most voltmeters have a very high resistance
• meaning the current they consume for a given pd is low
• as R = V / I

Question 6

what is an alternate way of setting up the circuit to measure the resistance of a resistor

Answer 6

• place the ammeter in the same channel as the resistor that is parallel to the voltmeter
• with the voltmeter now being in parallel to both of them

Question 7

what would this now do instead

Answer 7

• it would still be measuring the current in the resistor

- but the voltmeter will be measuring the pd across both the resistor and the ammeter

Question 8

why does the impact of the ammeter when reading the pd of the resistor usually get ignored

Answer 8

• ammeters are built to have low resistances
• so they dont affect the current they are measuring
• this means that using R = V / I, the pd they take up must be very small
• so it doesnt really matter

Question 9

rather than using ammeters and voltmeters to calculate the resistance, what can be used instead to measure the resistance of the resistor directly

Answer 9

a digital ohmmeter

Question 10

how does the ohmmeter measure the resistance

Answer 10

• when you turn the dial on a multimeter to the ohm range you bring a battery into play
• this produces a very small current in the component whose resistance is being determined
• this is measured by the meter and converted into a resistance reading