In circuit building a set of agreed symbols is in use worldwide to represent components.
(a)
For each description below, write the name and draw the correct symbol which would be used in a circuit diagram.
(i)
A resistor whose resistance depends on the light intensity.
[2]
(ii)
A component with zero resistance which measures the current in the circuit.
[2]
(iii)
The component which is used to convert ac current to dc current; it also allows current to flow in only one direction.
[2]
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(b)
In each case select the word to correctly describe an ammeter.
In a circuit the current/voltage/resistance is measured using an ammeter, which is always connected in series/parallel within a circuit.
An ideal ammeter should have very high/zero resistance. This prevents the ammeter taking any energy from the electrons/positive ions flowing through it.
If the electrons transferred their electricity/energy/motion to the ammeter this would change the circuit by reducing/increasing the value of the current it is meant to measure.
[3]
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A charge of 15.0 C passes through a resistor at a constant rate in 60 s. The potential difference across the resistor is 2.0 V.
(c)
Calculate the resistance R of the resistor.
[3]
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(d)
The resistance of a wire is affected by factors including the resistivity of the material it is made from.
(i)
Define resistivity.
[2]
(i)
State two other factors apart from temperature which affects the resistance of a wire. For each one identify whether the relationship is directly or inversely proportional to resistance.
[2]
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A student is building a circuit using three resistors, each with a value of 5.0 Ω. The student arranges the resistors first in series and then in parallel, as shown.
(a)
Determine the total resistance in each case.
(i)
Three 5.0 Ω resistors in series
[2]
(ii)
Three 5.0 Ω resistors in parallel
[2]
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The student arranges the identical 5.0 Ω resistors so that they are in a combination of series and parallel as shown.
(b)
Calculate the new combined resistance.
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An electrically-conducting wire is made from copper. Copper has resistivity ρ = 1.7 × 10–8 Ω m.
The wire has diameter d = 2.0 mm and length L = 20 mm as shown.
(c)
For the wire calculate
(i)
The cross-sectional area of the wire
[2]
(ii)
The resistance of the wire
[2]
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A student investigating the resistivity of a sample of wire has plotted a graph of resistance against length as shown.
(d)
Explain how the graph can be used to determine the resistivity of the wire.
[3]
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(a)
Define resistance.
[2]
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The simple circuit diagram shown illustrates Kirchoff's First Law.
(b)
State the law in words.
[2]
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(c)
For the circuit shown determine the values on the ammeters. A1 , A2 and A3 .
[3]
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(d)
For Kirchhoff's second law
(i)
State Kirchhoff's Second Law.
[2]
(ii)
Complete the sentence;
Kirchhoff's First Law is a consequence of the conservation of _____ while Kirchhoff's Second Law is a consequence of the conservation of _____.
[2]
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The graph shown represents current and potential difference for an Ohmic resistor.
a)
State the features of the graph which show that the resistor obeys Ohm's Law.
[2]
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A student investigating the I-V characteristics of various components plots the graph shown.
(b)
Outline how to find the resistance of the component from the graph.
[3]
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The graph shown represents the I-V characteristics of a non-Ohmic resistor such as a lamp.
(c)
The graph consists of three distinct parts.
(i)
For the section labelled (i) outline the behaviour of the resistor.
[2]
(ii)
For the two similar sections labelled (ii) outline the behaviour of the resistor.
[3]
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Heating is typically seen in electrical components and must be accounted for so that they operate safely and efficiently.
(d)
State two factors which increase the amount of heat output.
[2]
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(a)
For the series circuit shown, calculate
(i)
Total resistance.
[2]
(ii)
Current measured by the ammeter
[2]
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(b)
For the parallel circuit shown, calculate
(i)
Total resistance.
[2]
(ii)
Current measured by the ammeter
[2]
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The potential divider circuit shown is to be adapted to become a sensing circuit for temperature.
(c)
Suggest a change which would enable this.
[2]
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The sensing circuit in part (c) has been built using a thermistor placed in parallel to the output voltage, with a fixed resistor R1 of 100 Ω, and an input voltage, Vin of 220 V as shown.
At a certain temperature the thermistor has resistance R2 = 20 Ω.
(d)
Determine the output voltage at this temperature.
[3]
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