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New Senior Secondary Physics Compulsory: Electricity and Magnetism Chapter 2 Electric Circuit

CHAPTER 2 ELECTRIC CIRCUIT

1 Electric charges

Two kinds of charges

Who carry those charges?

Unit of charge

2 Flow of charge and electric current

The true picture of a circuit


The conventional picture of current

The two pictures are equivalent

Unit of current

[HKCEE][Charge calculation]

In the current in the circuit shown is 0.8 A, what is the number of electrons passing through the point X in 1minute? (The charge on each electron is 1.6 x 10-19C.)


3 Potential, voltage and Electromotive Force (EMF)

Why charge moves around in a circuit?

Potential, Voltage and Electromotive force of a source

Unit of voltage

[Conservation of energy][HKCEE] The potential difference between two points X and Y in a circuit is 10 V. Which of the following must be correct? A. 1 J of electrical potential energy is transferred in passing 10 C of charges from X to Y. B. 5 J of electrical potential energy is transferred in passing 2 C of charges from X to Y. C. 10 J of electrical potential energy is transferred in passing 1 C of charges from X to Y. D. The resistance between X and Y is 100. E. The current flowing through X and Y is 10 A.


4 Resistance

Ohm’s Law

Non-ohmic device

Factors affecting resistance

[HKCEE] [V-I graph and resistivity]

Figure (a) shows a circuit used to investigate how the potential difference V across a resistance wire varieswith the current I through the wire. The result is shown in Figure (b). If the experiment is repeated using athinner wire of the same material and of equal length, which of the following graphs (denoted by the dashedline) represents the expected result?


5 Electric circuit 5.1 Circuit components

Power supply Battery DC supply AC supply

Loads Light Bulb Resistor Rheostat (Variable resistor)

Measuring devices Ammeter Voltmeter

Switches Simple switch Reed Relay

Circuit controllers Fuse Diode Light Emitting Diode


5.2 Simple circuit

[Simple calculation] A light bulb is connected to a 3V battery. If the resistance of the light bulb is 2Ω, what is the current drawn from the battery?

5.3 Simple serial circuit

[Simple calculation] Two resistors AR and BR are connected to a 3V battery. If the resistance of AR is 2Ω and that of BR is

3Ω,

(a) what is the current drawn from the battery?

(b) what is the potential differences across AR and BR respectively?

Equivalent resistance for resistors in series


5.4 Simple parallel circuit

[Simple calculation] Two resistors AR and BR are connected to a 3V battery. If the resistance of AR is 2Ω and that of BR is

3Ω,

(a) what is the current drawn from the battery?

(b) what is the currents passing through AR and BR respectively?

Equivalent resistance for resistors in parallel


[HKCEE][Circuit]

Find the potential difference between X and Y in the above circuit.

[HKCEE][Circuit]

In the above circuit, all resistors are identical and the ammeters are of negligible resistance. If the reading ofammeter A1 is 2 A, find the readings of ammeter A2 and A3.


[HKCEE][Circuit]

In the above circuit, the reading of ammeter A1 is 0.6 A. (a) Find the potential difference between points P and Q. (b) Find the current drawn from the battery. (c) Find the electromotive force supplied by the battery. [HKCEE][Circuit]

In the above circuit, the ammeters are of negligible resistance. Which of the following statements is/are trueif switch S is closed? (1) The reading of ammeter A1 decreases. (2) The reading of ammeter A2 increases. (3) The reading of the voltmeter remains unchanged. A. (1) only B. (3) only C. (1) and (2) only D. (2) and (3) only E. (1), (2) and (3)


[HKCEE][Circuit]

In the above circuit, the reading of ammeter A2 is 0.3 A. Find the reading of ammeter A1.

[HKCEE][Equivalent resistance]

All the resistors in the above networks are identical. Arrange the networks in ascending order of equivalentresistances: A. (1), (2), (3) B. (1), (3), (2) C. (2), (1), (3) D. (3), (1), (2) E. (3), (2), (1)


[HKCEE][Circuit]

In the above circuit, the current delivered by the cell is I. What is the current passing through the 30 Ωresistor?

A. 1

2I B.

1

3I C.

1

4I D.

1

5I E.

4

5I

[HKCEE][Short Circuit]

If switch S in the above circuit is closed, which of the following statements is/are correct? (1) The readings of A1 and A2 are both increased. (2) The ratio of the readings of ammeter A1 and A2 is increased. (3) The reading of ammeter A3 remains unchanged. A. (1) only B. (3) only C. (1) and (2) only D. (2) and (3) only E. (1), (2) and (3)


6 Internal resistances of ammeter and voltmeter

Internal resistance of ammeter

Internal resistance of voltmeter

Circuit for measuring small and large resistance


[HKCEE] [Reliable circuit measurement] It is known that the resistance of a resistor R is about 5 kΩ. Which of the following circuits is most suitablefor measuring the resistance of R? The ammeter and voltmeter used are common moving coil meters.

[HKCEE] [Reliable circuit measurement]

A student uses the above circuit to find the resistance of a resistor R. Which of the following statements is/are correct? (1) The ammeter reading records the actual current passing through R. (2) The voltmeter reading records the actual potential difference across R. (3) The value of the resistance R obtained is smaller than its actual value. A. (1) only B. (3) only C. (1) and (2) only D. (2) and (3) only E. (1), (2) and (3) [HKCEE] [Short circuit]

A student uses an ammeter and a voltmeter to find the resistance of a light bulb. He incorrectly connects thecircuit as shown above. Which of the following is the most probable outcome? A. The ammeter burns out. B. The voltmeter burns out. C. The light bulb burns out. D. The reading of the ammeter is zero. E. The reading of the voltmeter is zero.


[HKCEE] [Circuit connection]

The above diagram shows an experimental set-up for measuring the resistance of a bulb. To which of theterminals P, Q and R of the ammeter and voltmeter should each of the wires be connected?


7 Internal resistance of battery EMF and terminal voltage

[HKALE (simplified)] [Internal resistance]

The figure above shows part of a circuit which carriesof 1 A from Yto Xthrough a cell of e.m.f. 3 V andinternal resistance 1 Ω. The potential differencebetween X and Y is A. 0 V. B. 1 V. C. 2 V. D. 3 V. E. 4 V.

8 Serial and parallel connection of batteries

Batteries connected in series


Batteries connected in parallel

FINAL REMARKS

The study of electricity and magnetism starts with its most common application in electric circuits. The concepts of charge, electric current, voltage and resistance are developed and circuit analyzing techniques are covered. Students are expected to master the calculation involved in electric circuit. The two basic principles of analyzing circuits are:

1. Current must be conserved along a path. 2. Points joined directly by wires must have the same potential.

Some characteristics of the internal resistances of ammeter and voltmeter are introduced. Students should aware their effects in circuits, especially in designing circuits for measuring unknown resistance.

em02 electric circuit - kotze223.files.wordpress.com · factors affecting resistance [hkcee] ... 7...

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