4.3.2a Series circuits

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Question 1

An investigation is carried out on circuits containing different combinations of two identical resistors, $R_1$ and $R_2$ .

Circuit A: Resistors $R_1$ and $R_2$ are connected in parallel between two terminals, P and Q.
Circuit B: Only resistor $R_1$ is connected between terminals P and Q.
Circuit C: Resistors $R_1$ and $R_2$ are connected in series between terminals P and Q.

The table below shows the measurements of potential difference $V$ across terminals P and Q, and the current $I$ in each circuit:

Circuit	$VV\text{ / V}$	$AI\text{ / A}$
Circuit A	$1.2$	$0.80$
Circuit B	$1.8$	$0.62$
Circuit C	$2.4$	$0.41$

Calculate the resistance $R$ for each circuit using the equation:

\frac{V}{I}

Give your answers to a consistent 2 or 3 significant figures.

[3]

Estimate the resistance of a single resistor by calculating $RAR_{\text{A}}$ , $RBR_{\text{B}}$ , and $RCR_{\text{C}}$ [edit] using the expressions:

$RA=2RR_{\text{A}} = 2R$ (using the value of $R$ from Circuit A)
$RB=RR_{\text{B}} = R$ (using the value of $R$ from Circuit B)
$RC=R2R_{\text{C}} = \frac{R}{2}$ (using the value of $R$ from Circuit C)

[2]

State whether your results support the suggestion that $RAR_{\text{A}}$ , $RBR_{\text{B}}$ , and $RCR_{\text{C}}$ should be equal. Justify your statement by referring to your values.

[1]

The circuits are powered by a supply voltage. A fixed protective resistor, $ΩR_{\text{P}} = 3.0\ \Omega$ , is placed in series with the combination of resistors between P and Q. Explain why this resistor is necessary to protect the circuit, referring to what would happen to the current if $RPR_{\text{P}}$ [edit] were removed when testing Circuit A.

[3]

Describe the circuit symbol for a variable resistor (rheostat).

[1]

State one advantage of using a variable resistor in this experiment rather than regularly changing the supply voltage to obtain multiple readings.

[1]

Circuit

VV\text{ / V}

AI\text{ / A}

ΩR\text{ / }\Omega

Circuit A

1.2

0.80

Circuit B

1.8

0.62

Circuit C

2.4

0.41

4.3.2a Series circuits

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4.3.2a Series circuits Questions

4.3.2a Series circuits

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4.3.2a Series circuits Questions