2019 A/L Physics Past Paper · Question 26 (English Medium)

Answer: (3) $1.4\ \text{V}$

What the question asks

We want:

The reading of the multimeter in the figure.

We use the selector knob, the terminals and the pointer.

Relevant theory

An analogue multimeter has one moving coil meter.

Different series and shunt resistances make it a voltmeter, an ammeter or an ohmmeter.

The selector knob sets the job and the range.

The pointer shows a fraction of the scale.

The reading is that fraction times the range.

The instrument which is been used as the ammeter to measure electric currents is the moving coil galvanometer which has been calibrated accordingly.

Applying it to this question

The things in the figure:

The scales: $\Omega$, DCV·A with 0–10, 0–50 and 0–250, and ACV·A.

The pointer.

The selector knob.

Three terminals: $2\ \text{A}$, $+\text{V/mA/}\Omega$ and $-\text{COM}$.

The connections:

The leads are in the $+\text{V/mA/}\Omega$ and $-\text{COM}$ terminals.

The $2\ \text{A}$ terminal is not used.

The knob points to $2\ \text{V}$ in the DC V part.

Which scale?

It is DC V, so we use the DCV·A scale.

For the 2 V range the 0 to 10 scale is easiest. The number 10 stands for 2 V.

The pointer is between 6 and 8. It is at 7.

Reasoning and calculation

The rule:

Divide the pointer number by 10.

Multiply by the range.

$0.7$

$\frac{7}{10}$

$1.4$

$V = 0.7 \times 2\ \text{V}$

Reading the options

The reading is $1.4$ V. That is option (3).

Why the other options fail

It reads the resistance scale.

It reads a current.

It takes the scale number as volts.

It takes the range as 20 V.

Checks

Does it make sense?

On the 2 V range the reading cannot be more than 2 V.

The pointer is at 70 % of the scale. So $1.4$ V is right.

7 V and 14 V are not possible on this range.

Conclusion

$V = 1.4\ \text{V}$

The knob is on DC V, range 2 V.

The pointer is at 7 on the 0 to 10 scale.

$$\dfrac{7}{10} \times 2 = 1.4\ \text{V}$$

The answer is option (3).

On a multimeter, look at the knob first.

It tells what is measured and the range.

Then pick the scale that suits the range.

Exam tip