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Study B.5 Current and circuits conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

[Maximum number: 7]

(a)

A cell is connected to an ideal voltmeter, a switch S and a resistor R. The resistance of R is $4.0 \Omega$ .

When S is open the reading on the voltmeter is 12 V . When S is closed the voltmeter reads 8.0 V .

[ 3 ]

(i)

State the emf of the cell.

[ 1 ]

$12 \vee$

(ii)

Deduce the internal resistance of the cell.

[ 2 ]

I=2.0 A OR 12=I(r+4) OR 4=I r OR 8=4 I

«Correct working to get » r=2.0 « $\Omega$ »

Marking guidance:

Allow any valid method.

Allow ECF from (b)(i)

(b)

A fully charged cell of emf 6.0 V delivers a constant current of 5.0 A for a time of 0.25 hour until it is completely discharged.

The cell is then re-charged by a rectangular solar panel of dimensions $0.40 \mathrm{~m} \times 0.15 \mathrm{~m}$ at a place where the maximum intensity of sunlight is $380 \mathrm{Wm}^{-2}$ .

The overall efficiency of the re-charging process is 18 %.
Calculate the minimum time required to re-charge the cell fully.

[ 3 ]

ALTERNATIVE 1 «energy output of the panel = » VIt OR $6 \times 5 \times 0.25 \times 3600$ OR 27000 «J»

«available power = » $380 \times 0.4 \times 0.15 \times 0.18$ OR 4.1 «W»
$t=\ll \frac{27000}{4.1}=>6600<\mathrm{s} \gg$

ALTERNATIVE 2

«energy needed from Sun = » $\frac{V I t}{e f f}$ OR $\frac{6 \times 5 \times 0.25 \times 3600}{0.18}$ OR 150000 «J» « incident power=» $380 \times 0.4 \times 0.15$ OR 22.8 «W»
$t=\ll \frac{150000}{22.8}=>6600<\mathrm{S} \gg$

Marking guidance:

Allow ECF for MP3

Accept final answer in minutes (110) or hours (1.8).

(c)

Outline why research into solar cell technology is important to society.

[ 1 ]

[Maximum number: 3]

This question is in two parts. Part 1 is about solar power and climate models. Part 2 is about digital storage of data.

(a)

Distinguish, in terms of the energy changes involved, between a solar heating panel and a photovoltaic cell.

[ 2 ]

(b)

State an appropriate domestic use for a

[ 1 ]

(i)

photovoltaic cell.

[ 1 ]

[Maximum number: 6]

This question is in two parts

(a)

The plates in (c) are replaced by a cell that has an emf of 12.0 V and internal resistance $5.00 \Omega$ . A resistor of resistance R is connected in series with the cell. The energy transferred by the cell to an electron as it moves through the resistor is $1.44 \times 10^{-18} \mathrm{~J}$ .

[ 6 ]

(i)

Define resistance of a resistor.

[ 1 ]

ratio potential difference/voltage (across resistor) to current (in resistor) / $\frac{V}{I}$
with symbols defined;

(ii)

Show that the value of R is $15.0 \Omega$ .

[ 4 ]

pd across $R=\frac{1.44 \times 10^{-18}}{1.6 \times 10^{-19}}=9.00 \mathrm{~V}$ ;
pd across internal resistance $=12.0-9.00=3.00 \mathrm{~V}$ ;
current in circuit $=\frac{3.00}{5.00}=0.600 \mathrm{~A}$ ;
$R=\frac{9.00}{0.600}=15.0 \Omega$ ;

(iii)

Calculate the total power supplied by the cell.

[ 1 ]

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IB Physics HL B 5 Current and Circuits Topic Practice

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