7.3 Series n Parallel 2013

7/30/2019 7.3 Series n Parallel 2013

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7.3 SERIES AND PARALLEL CIRCUITS | DATE: ..

An Electrical Joke

An apparatus in the form of a chair, used in

electrocuting persons sentenced to death

A chemist, a biologist and an electrical engineer were on death row waiting to go in the electric chair.

The chemist was brought forward first. 'Do you have anything you want to say?' asked the

executioner, strapping him in.

'No,' replied the chemist. The executioner flicked the switch and nothing happened. Under this

particular State's law, if an execution attempt fails, the prisoner is to be released, so the chemist was

released.

Then the biologist was brought forward. 'Do you have anything you want to say?'

'No, just get on with it.' The executioner flicked the switch, and again nothing happened, so the

biologist was released.

Then the electrical engineer was brought forward. 'Do you have anything you want to say?' asked the

executioner.

'Yes,' replied the engineer. 'If you swap the red and the blue wires over, you might make this thing

work.'

[email protected] f52013 26


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Comparison between series and parallel circuit

SERIES CIRCUIT PARALLEL CIRCUIT

Arrangementofapparatus

Label ammeter, A1, voltmeter, V1, V2, and V3, Label ammeter, A, A1, A2 and A3,

Effective

Resistance,R

Current, I

Voltage, V

If resistors are identical, 2 , calculate:

(a) Effective resistance, R(b) Main current, I(c) Current through each resistor(d) Voltage across each resistor

If resistors are identical, 2 , calculate:

(a) Effective resistance, R(b) Main current, I(c) Voltage across each resistor(d) Current through each resistor



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AMMETER READING CURRENT

VOLTMETER READING POTENTIAL DIFFERENCE VOLTAGE



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EFFECTIVE RESISTANCE, R(a)

(Ans: 35)

(b)

(Ans: 1.25)

(c)

(Ans: 34)

(d)

(Ans:3.2)

(e)

(Ans: 2.33)

(f)

(Ans: 5)



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SOLVE PROBLEMS USING V = IR: Solve the unknown values, R, I or V

(Ans: 0.5) (Ans: 20)

(Ans: 10) (Ans: 2.4)



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Brightness of bulb(s)

Circuit 1In a series circuit, two or more resistors are

connected one end after another to form a

_____________ path for current flow.

Draw the circuit

The bulbs _____________ the potentialdifference from the battery, so each glows

dimly. The brightness of each bulb is equally the

same since the same _____________ flowsthrough each bulb.

If one bulb is removed, the other_____________ _____________ because thecircuit is broken.

Circuit 2In a parallel circuit, all components are connected

with their corresponding ends joined together to

form _____________ and parallel paths for currentflow.

Draw the circuit.

Each bulb gets the full __________________________ from the battery becauseeach is connected directly to it.

A __________ current flow through each bulb,so each bulb glows brightly.

The brightness of each bulb in a parallelcircuit is _____________ than those in aseries circuit with the same number of bulbs.

If one bulb is removed, the other keeps_____________ because it is still part of anunbroken circuit.

Circuit 3

P, Q and R are identical.

Compare brightness P, Q and

R.

Circuit 4

X, Y and Z are identical.

Compare brightness X, Y and Z.

Circuit 5

S and T are identical. Compare

brightness of S and T if

(i) switch is opened(ii) switch is closed



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*Clue The greater the current flow, the brighter the bulb



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EXERCISE 7.31.

Three resistors are connected in

series to a 6 V battery.

(Ans (c) 1V, 2V, 3V)

Calculate

(a) the effective resistance, R of the circuit,

(b) the current, I in the circuit

(c) The potential difference across each resistor,V1, V2, and V3.

2.

An 8 resistor and a 12 resistor

are connected with a 12 V battery.

What is the potential differenceacross

(Ans: (a) 4.8V)

(a) 8 resistor (b) 12 resistor

3 The three resistors are connected inparallel to the battery.

Calculate

(a) the potential differenceacross each resistor

(b) the effective resistance(c) the ammeter reading(d) the current passing through

each resistor.

(Ans: 3A, 1.5A, 1A)



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4. A potential difference of 3 V isapplied to a network of resistors.

(a) What is the effectiveresistance of the circuit?

(b) What is the reading of theammeter?

(c) What is the voltage acrossthe parallel network?

(d) What is the current flowingthrough the 6 resistor?

(Ans: 6, 0.5,1.0, 0.17)

5. In the circuit shown, what is the reading on theammeter when switch, S

(a) is open? (b) is closed?

(Ans:2.0, 3.0)



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6. Determine the voltmeter reading.(a)

(c)

Determine the ammeter reading.

(b)

(Ans: 16, 0.25, 1.5)

7.

Calculate

(a) The effective resistance, R

(b) The main current, I

(c) The current passing through 8 and 2.5

resistors.

(d) (i) The potential difference across 8

resistor.

(ii) The potential difference across 2.5

resistor.

(e) The current passing through 6

resistor.

(Ans: (a)12 (b) 2 (d)16 (e)0.5)



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EXERCISE 7.3: OBJECITVE Qs

1 The figure shows ammeter reading in acircuit. Which ammeter is showing a

faulty reading?

2 A battery lights all four lamps as shown inthe following figure. Which lamp, if

removed, would cause all the lamps to

light off?

3 Which of the bulbs in the following figureis the brightest? Given that all the bulbs

are identical.

4 The figure shows the resistorcombinations P, Q and R.

Which resistor combination has the

lowest and the highest resistance?

Lowest

resistance

Highest

resistance

A. Q PB. R PC. R QD. P R

5 Which resistor combination gives the

effective resistance 8 ?



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6. A current flows in two resistors connectedin series as shown in the following figure.

A1 and A2 are the readings on ammeter

V1 and V2 are the readings on the

voltmeters.

Which of the following is correct?

Ammeter reading Voltmeter reading

A A1 < A2 V1 < V2B A1 < A2 V1 > V2C A1 = A2 V1 > V2D A1 = A2 V1 < V2

7. A current flows towards the junction oftwo resistors connected in parallel as

shown in the following figure. A1 and A2

are the readings on ammeter V1 and V2

are the readings on the voltmeters.

Which of the following is correct?

Ammeter reading Voltmeter reading

A A1 < A2 V1 > V2B A1 < A2 V1 = V2C A1 = A2 V1 < V2

D A1 > A2 V1 = V2

8. The diagram shows a circuit.

What is the reading of the ammeter when

the switch, S is opened and closed?

Switch S

is opened

Switch S is

Closed

A 4.0 A 6.0 AB 2.0 A 6.0 AC 2.0 A 3.0 AD 2.0 A 1.2 A

9. Two resistors 4 is connected parallel asshown in Figure (a) and the current I1

flows. Later, the resistor resistors 4 is

connected series l as shown in Figure (b)

and the current I2 flows.

What is the ratio I1: I2?



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A 1 : 2 B 1 : 4C 2 : 1 D 4 : 1

10. The diagram shows a circuit.

What is the value of current I1 and I2 ?

A I1 = 0.4A I2 = 0.4 AB I1 = 2.0A I2 = 0.5 AC I1 = 0.5A I2 = 2.5 AD I1 = 2.5A I2 = 2.5 A

11.

What is the reading of the voltmeter in the

circuit above when the switch is closed?

A 8.0 V B 7.8 VC 6.8 V D 5.8 V

12 The diagram shows a circuit.

What is the potential difference across

the resistor2 ?

A 2 V B 4 VC 6 V D 8 V



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EXERCISE 7.3: STRUCTURED Qs

1 The figure shows a circuit consisting of 3 identical resistors X, Y, Z and two measurementinstruments P and Q.

(a) Name the measurement instruments,P : _______________________

Q : _______________________

(b) (i) When an identical resistor is connected parallel to resistor Z, what happen to the reading of

P and Q?

P : _______________________

Q : _______________________

(ii) Give the reason for your answer in (b)(i).

(c) The resistorsX, Y and Z are replaced by three identical bulbs K, L and M as shown infollowing figure.

Compare the brightness between the bulbs

(i) K and L : _______________________

(ii) L and M : _______________________


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7.3 Series n Parallel 2013