“D.C CIRCUITS”

Combined Science 5129BENGKEL KECEMERLANGAN AKADEMIK 2015

CURRENT & POTENTIAL DIFFERENCE IN CIRCUITSSERIES & PARALLEL CIRCUITS

LEARNING OUTCOMES

CIRCUIT SYMBOLS

CURRENT“The rate of flow of charges in a circuit”

CURRENT CHARGE

TIME=

S.I unit of current is the Ampere ( A )Other unit of current is Coulomb/Second (C/s)

An ammeter is used to measure the current in a circuit.

CURRENT IN SERIES CIRCUIT

A

A A

A1

2 3

4

Current is the same everywhere in a series circuit.

I1 I2 I3 I4= = =

CURRENT IN PARALLEL CIRCUIT

A1

A2

A3

A4

A5

= I5I2 I3 I4= +I1 +

Current in the main branch is the sum of

current in each branch.

CURRENT IN PARALLEL CIRCUIT

A1

A2

A3

A4

A5

Branch with the highest resistance will

have the smallest current.

POTENTIAL DIFFERENCE“The amount of energy needed to move a unit

charge across a component in a circuit.”

POTENTIAL DIFFERENCE ENERGY

CHARGE=

S.I unit of potential difference is the Volt ( V )Other unit of potential difference is Joule/Coulomb ( J/C )

A voltmeter is used to measure the potential difference across an electrical component.

POTENTIAL DIFFERENCE IN SERIES CIRCUIT

The sum of the potential difference (pd) across each of the components of the circuit is equal to the potential

difference across the cell.

V1 V2 V3 V4= + +

V3 V4V2

V1

POTENTIAL DIFFERENCE IN SERIES CIRCUIT

Component with the highest resistance will have the highest potential difference

across it.

V3 V4V2

V1

POTENTIAL DIFFERENCE IN PARALLEL CIRCUIT

In a parallel circuit, the potential difference (pd) across all the branches are the same.

V1 V2 V3 V4= = =

V3 V4V2V1

RESISTANCE“The measure of the degree to which an electrical

component opposes the flow of an electric current.”

High Resistance, Low Current,

High Potential Difference

Low Resistance, High Current,

Low Potential Difference

An electrical conductor that has:

through it.

RESISTANCE POTENTIAL DIFFERENCE

CURRENT=

S.I unit of resistance is the Ohm ( Ω )

FUNCTION OF RESISTORS

Resistors in a circuit

Main function is to control

the amount of current flowing

in a circuit.

RESISTORS IN SERIES

R RR1 2 3

The total resistance is the sum of each resistance in the series circuit.

R TOTAL R1 R2 R3= + +

MORE resistors in series, HIGHER total resistance.

RESISTORS IN PARALLEL

R1

R2

R3

MORE resistors in parallel, SMALLER total resistance.

R TOTAL R1 R2 R3= + +

1 1 1 1

EXAMPLE EXERCISE 15129/12/M/J/12 Q36

A resistor in a circuit has a value of resistance of 3.0 Ω.

In 20 s, a charge of 10 C passes through the resistor.

What is the potential difference across the resistor?

EXAMPLE EXERCISE 25129/22/M/J/14 Q3

A circuit diagram containing two lamps P and Q is shown in Fig.3.1.

(a) Calculate the resistance

of lamp P.

The switch is closed, the current in lamp P is 0.3 A and the potential difference across it is 6 V.

EXAMPLE EXERCISE 25129/22/M/J/14 Q3

A circuit diagram containing two lamps P and Q is shown in Fig.3.1.

(b) The current in lamp Q is 0.2 A.

Determine the current in the circuit at:

(i) Point A

(ii) Point B

(iii) Point C

EXAMPLE EXERCISE 35129/12/O/N/13 Q35

A series circuit consists of a battery, an ammeter, a lamp and a resistor. A voltmeter is placed across the lamp and the resistor.

What is the voltmeter reading?

EXAMPLE EXERCISE 4Fig.11.1 shows a lighting circuit.

5129/22/M/J/13 Q11

(c) When all the switches are closed to light both lamps, the current in lamp P is 0.25 A and the current in lamp Q is 0.35 A

(i) Calculate the current in the fuse.

EXAMPLE EXERCISE 55129/12/M/J/13 Q37

A circuit consists of a battery and four resistors. The current in three of the resistors is shown.

What is the current in X?

EXAMPLE EXERCISE 65129/22/O/N/12 Q11

Fig.11.1 shows a series circuit. A voltmeter measures the potential difference (p.d) across the 2.0 Ω resistor.

(a) The variable resistor is adjusted so that the

voltmeter reads 1.0 V.

(i) Calculate the current in the 2.0 Ω resistor.

EXAMPLE EXERCISE 65129/22/O/N/12 Q11

Fig.11.1 shows a series circuit. A voltmeter measures the potential difference (p.d) across the 2.0 Ω resistor.

(a) The variable resistor is adjusted so that the

voltmeter reads 1.0 V.

(ii) The p.d across the battery terminals is 5.0 V. The voltmeter reads 1.0 V.

Calculate the p.d across the variable resistor.

EXAMPLE EXERCISE 65129/22/O/N/12 Q11

Fig.11.1 shows a series circuit. A voltmeter measures the potential difference (p.d) across the 2.0 Ω resistor.

(b) The resistance of the variable resistor is increased.

(i) the current in the variable resistor

(ii) the p.d across the 2.0 Ω resistor

State what happens, if anything, to:

PRACTISE QUESTIONS

5129/12/O/N/14 Q37

Complete the following questions in pairs.

5129/12/O/N/14 Q38

5129/22/O/N/14 Q14

Remember to raise your hands if you needed help with the question.