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2.4 More problem solving by directly comparing simple circuit diagrams

(some simple current deductions or calculations)

Unless otherwise stated, the bulbs are identical resistors and the individual cells (batteries) are identical too.

The cell/lamp ratio is equal to the p.d/resistance ratio (or vice versa). p.d. = potential difference in volts.

Lamp resistance are added together when wired in series.

Similarly, the total p.d. (voltage) equals the sum of the cells when wired in series.

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Q1.

From the four circuits shown:

(a) In which two circuits will the bulb/bulbs be the same brightness?

(b) In which circuit/circuits will the lamps glow the dimmest?

(c) In which circuit/circuits will the lamps glow the brightest?

ANSWERS

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Q2.

From the four circuits shown

(a) Which two circuits will have the same brightness?

(a) Which circuit will have the brightest lit lamp or lamps'?

(c) Which circuit will have 'the dimmest lit lamp/lamps?

ANSWERS

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Q3.

From the four circuits shown:

(a) In which two 'will the lamps be the same brightness'?

(b) Which circuit/circuits will have the brightest lit lamp/lamps?

(c) Which circuit will have the dimmest lamp/lamps?

ANSWERS

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Q4.

The five circuits show various arrangements of identical cells and identical batteries.

(a) If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.6A?

(b)  If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.15A?

(c) If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.9A

(d) If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.1A?

ANSWERS

INDEX of notes on drawing and interpreting simple electrical circuits

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Keywords, phrases and learning objectives for simple electrical circuits

Know how to solve simple problem solving by directly comparing simple circuit diagrams/

In simple circuits, be able to deduce which bulbs light up and lamps glow more or less brightly by comparing two or more circuit diagrams of lamps.

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INDEX of notes on drawing and interpreting simple electrical circuits

ANSWERS TO CIRCUIT DIAGRAM PROBLEMS

Q1.

From the four circuits shown:

(a) In which two circuits will the bulb/bulbs be the same brightness?

Answer: Circuits 01 and 05, same ratio of cells to lamps (same resistance/lamp ratio)

(b) In which circuit/circuits will the lamps glow the dimmest?

Answer: Circuit 04, the highest lamp/cell ratio, more lamps in series, bigger resistance to current flow.

(c) In which circuit/circuits will the lamps glow the brightest?

Answer: Circuit 07, highest cell/lamp ratio (highest p.d./resistance ratio), in fact highly likely to blow the bulb.

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Q2.

From the four circuits shown

(a) Which two circuits will have the same brightness?

Answer: Circuits 03 and 16, same cell/lamp ratio (same p.d./resistance ratio).

(a) Which circuit will have the brightest lit lamp or lamps'?

Answer: Circuit 07, the highest cell/lamp ratio (highest p.d./resistance ratio).

(c) Which circuit will have 'the dimmest lit lamp/lamps?

Answer: Circuit 09, the lowest cell/lamp ratio (lowest p.d./resistance ratio).

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Q3.

From the four circuits shown:

(a) In which two 'will the lamps be the same brightness'?

Circuits 04 and 17, same cell/lamp ratio (same p.d./resistance ratio)

(b) Which circuit/circuits will have the brightest lit lamp/lamps?

Circuit 06, highest cell/lamp ratio (highest p.d./resistance ratio).

(c) Which circuit will have the dimmest lamp/lamps?

Answer: Circuit 08, the lowest cell/lamp ratio (lowest p.d./resistance ratio)

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Q4.

The five circuits show various arrangements of identical cells and identical batteries.

(a) If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.6A?

Answer: Circuit 03, same p.d., but 1 bulb, half the resistance of circuit 02

(b)  If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.15A?

Answer: Circuit 04, same resistance of 2 lamps, but half the p.d. of circuit 02

(c) If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.9A

Answer: Circuit 07, 1.5 x p.d and half the resistance, so current 3x that of circuit 02.

(d) If the ammeter reading in circuit 02 is 0.3A, in which circuit will the ammeter reading be 0.1A?

Answer: Circuit 08, half the p.d. and 1.5 x the resistance of circuit 02, 1/3 current flow

INDEX for notes on drawing and interpreting simple electrical circuits

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