Circuits

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

CHECKPOINT By the end of the lesson, students should be able to: Circuits
Identify the difference between series and parallel circuits
Compare parallel and series circuits in terms of voltage across components and current through them Voltmeters and Ammeters
Identify uses of ammeters and voltmeters
Explain why ammeters and voltmeters are connected differently in a circuit
Explain why there are different circuits for lighting, heating and other appliances in a house

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 2 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

CIRCUITS In last week’s work, we looked at the fundamental quantities in electrical circuits- Voltage, Current and Resistance – and the relationship between them: ܸ = ‫ܴܫ‬. In this week’s lesson we look at how the voltage and current varies through circuits connected in series and parallel.

WHAT ARE CIRCUITS? A circuit provides a pathway for electricity to flow. While there may be many different types of circuits, all circuits have some common properties and features: •

A source of potential difference or voltage (this is commonly the 240V mains supply)

•

A pathway for the electricity to flow. This must be through a conductor and is usually connecting wires. A load of some sort (resistor, bulb etc.) that consumes energy.

•

USING CIRCUIT DIAGRAMS Before examining circuits in greater detail, we first need to be familiar with how to read and interpret circuit diagrams. There are certain conventions and symbols that you need to know in order to understand circuit diagrams properly.

240 V

~

Connecting

Joined Wires

A

AC supply

Ammeter

Fuse

Bulb

V Voltmeter

Wire Wires

crossing

(no connection)

+

-

+

-

+

Switch

or

Cell

2 cells

Any number of cells

TALENT 100: HSC SUCCESS. SIMPLIFIED.

Resistor

www.talent-100.com.au Page 3 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

OPEN, CLOSED AND SHORT CIRCUITS There are 3 terms which we can describe any circuit: Open circuit – an open circuit is one that is not complete. This means that there is no complete connection between the two points with a potential difference. , and therefore current does not flow from one terminal to the other.

Closed circuit – A closed circuit is a circuit in which there are no breaks in the circuit, and therefore there is a complete connection between the two terminals that have a potential difference. This means all wires are connected, all switches are closed and current is able to flow through it.

Short circuit – Electricity takes the path of least resistance, so where electricity can flow through multiple paths, it will favour the path that has the lowest resistance, and is termed a ‘short circuit’.

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 4 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

Question 1 Explain why a person sitting in a bathtub who drops a hairdryer is likely to get an electric shock? …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………

SERIES CIRCUITS KEY FEATURES OF SERIES CIRCUITS The diagram below shows a circuit connected in series, with three resistors.

ܴଵ

ܴଶ

ܴଷ

Some of the key features of the circuit are that: •

All devices are connected in one loop so there is only one pathway for the current to follow

•

The current throughout the circuit and each device is constant

•

The sum of the potential drops across all resistors must be equal to the emf of the source (Kirchhoff’s Voltage Law)

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 5 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

VOLTAGE IN A SERIES CIRCUIT For resistors in a circuit connected in series, the sum of the potential drops across all resistors must be equal to the emf of the source.

Voltage in a Series Circuit

ܸ௧௢௧௔௟ = …………………………………………………………………… We can understand this by considering the Law of Conservation of Energy and remembering our first principles definition of Voltage. Voltage is a measure of the amount of energy per unit of charge, i.e. the amount of energy an electron moving through the circuit can give to each of the loads/resistors.

Each time an electron passes through a resistor, it must give up a certain amount of energy, and each time it passes through the battery or power source , it gets given a certain amount of energy. The law of conservation of energy states that the amount of energy it is given must be used up by the time the electron has moved through the entire circuit. If it does not, then it will continue to gain energy as it passes the supply emf and hence create infinite kinetic energy.

CURRENT IN A SERIES CIRCUIT Current measures the rate at which charges flow through a circuit. Since there is only one path for the current to move through, the current must be the same through all resistors.

Current in a Series Circuit

‫ܫ‬ଵ = …………………………………….

Talent Tip: The analogy of current in water streams or rivers, and current in electrical circuits breaks down here. Where as rocks may cause the water to slow down in a river, resistance in an electrical circuit does not cause electrons to slow down, but rather to give up more energy.

Because there is only one pathway to follow in a series circuit, if any component breaks or a wire is disconnected, current can no longer flow through the circuit. This makes this type of circuit unreliable as one small fault can cause larger problems.

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 6 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

RESISTANCE IN A SERIES CIRCUIT The effective resistance of a circuit with 3 resistors in series is shown below:

Resistance in a Series Circuit

ܴ௡௘௧ = ……………………………………………………………………

Question 2 (Conceptual) Given that: •

ܸ = ‫ܴܫ‬

•

ܸ௡௘௧ = ܸଵ + ܸଶ + ܸଷ

•

‫ܫ‬௡௘௧ = ‫ܫ‬ଵ = ‫ܫ‬ଶ = ‫ܫ‬ଷ

Show that ்ܴ = ܴଵ + ܴଶ + ܴଷ …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 7 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

Question 3 Calculate the current, voltage and resistance through each of resistor. a) 1ߗ

2ߗ

12V

STEP 1: Calculate the net resistance: ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… STEP 2: Calculate the net current using the net resistance: ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… STEP 3: Calculate the voltage drop by applying ohm’s law ܸ = ‫ ܴܫ‬to each resistor. ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 8 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

b) 5ߗ

5ߗ

40V

STEP 1: Calculate the net resistance: ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… STEP 2: Calculate the net current using the net resistance: ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… STEP 3: Calculate the voltage drop by applying ohm’s law ܸ = ‫ ܴܫ‬to each resistor. ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 9 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

c) 2ߗ

3ߗ

4ߗ

117V

STEP 1: Calculate the net resistance: ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… STEP 2: Calculate the net current using the net resistance: ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… STEP 3: Calculate the voltage drop by applying ohm’s law ܸ = ‫ ܴܫ‬to each resistor. ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 10 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

PARALLEL CIRCUITS KEY FEATURES OF PARALLEL CIRCUITS The diagram below shows a circuit connected in parallel:

‫ܫ‬ଵ

‫ܫ‬

‫ܫ‬ଶ

‫ܫ‬ଷ

ܴଵ

‫ܫ‬ ܴଶ

ܴଷ

Some of the key features of a circuit connected in series are that: •

There is more than one pathway for current to flow

•

All devices in the circuit have the same voltage across them

•

The sum of the current slowing into a point in circuit equals the sum of the current flowing out of that point (Kirchhoff’s Current Law)

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 11 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

CURRENT IN A PARALLEL CIRCUITS Current measures how many charges flow through a point in a particular second. Hence, the current through the power of supply equals the sum of the currents:

Current in a Parallel Circuit

‫………………………………………… = ܫ‬.

Let’s consider how this works. Suppose that for a particular circuit, 20 electrons flow through the circuit per second. Hence, when the current gets to a junction, such as at point A, in one second, there are 20 electrons. Each of these electrons can only go through one of three paths.

10݁

ܴଵ

20 ݈݁݁ܿ‫ݏ݊݋ݎݐ‬4݁ ܴଶ

6݁ ܴଷ

Hence the sum of the electrons through each of the paths must be equal to the number of electrons at the junction. This is known as the junction rule: the sum of the current going into a junction is equal to the current going out of the junction. The number of electrons that go through a particular branch is determined by the resistance. Electricity follows the path of least resistance. Therefore, more electrons (and hence more current) will go through the path of lower resistance than of higher resistance.

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 12 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

VOLTAGE IN A PARALLEL CIRCUITS Voltage measures the amount of energy that each charge has. This does not change simply because the charges go through one part of a circuit rather than through another part. Returning to our previous example, 10 electrons might go through the top, 4 through the middle and 6 through the bottom. However, all of these electrons have the same amount of energy. Hence:

Voltage in a Parallel Circuit ܸ = …………………………………………………………

These circuits are much more reliable than series circuits because if one of the resistors or leads breaks current can still flow through the other pathways and the circuit is still closed.

RESISTANCE IN A PARALLEL CIRCUITS The resistance of resistors in parallel circuits can be found by using:

Resistance in a Parallel Circuit ଵ ோ೙೐೟

= ……………………………………………………………………

ଵ

Talent Tip: Don’t forget to invert ோ to get the net resistance! ಿ

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 13 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

Question 4 (Conceptual) Given that: •

ܸ = ‫ܴܫ‬

•

ܸ௡௘௧ = ܸଵ = ܸଶ = ܸଷ

•

‫ܫ‬௡௘௧ = ‫ܫ‬ଵ + ‫ܫ‬ଶ + ‫ܫ‬ଷ

Show that

ଵ ோ೙೐೟

=

ଵ ோభ

+

ଵ ோమ

+

ଵ ோయ

…………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 14 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

Question 5 For the following circuits: a) The voltage through each of the resistors. b) The equivalent resistance of the circuit c) The current flowing in and out of the power source d) The current through each resistor.

1ߗ

2ߗ

12ܸ

…………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… www.talent-100.com.au TALENT 100: HSC SUCCESS. SIMPLIFIED. Page 15 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

…………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 16 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

5ߗ

5ߗ

40ܸ

…………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 17 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

1ߗ

2ߗ

……………………………………………………………………………………………………………………………………………………………

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 18 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

2ߗ

3ߗ

4ߗ

117V

…………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………………… TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 19 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

COMPOSITE CIRCUITS Sometimes you will encounter circuit with both series and parallel parts to it. This makes it difficult to calculate total resistance. However it can be done systematically by calculating the resistance for each component separately

Question 6 (11 marks) For the following circuit find: 12 ܸ

2ߗ 1ߗ

3ߗ

4ߗ

a) The equivalent resistance of the whole circuit

3

……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 20 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

b) The current through the first resistor

2

……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………

c) The voltage drop through the first resistor

2

……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………

d) The voltage drop across the parallel resistors

1

……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………

e) The current through each of the parallel resistors

3

……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 21 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

MEASURING CURRENT AND VOLTAGE AMMETER An ammeter is a device used to measure current in a circuit. Ammeters must be connected in series, since the current through all resistors connected in series is the same. If it were connected in parallel, the current would split, and only a portion of the current would go through the ammeter, giving an inaccurate reading. Ammeters must have low resistance so as not to affect the resistance of the circuit. If the ammeter had a high resistance, it would draw a lot of voltage and affect the circuit.

VOLTMETER Voltmeter is device which measures the voltage drop across a component. Since the voltage across resistors connected in parallel is the same, voltmeters are connected in parallel. Voltmeters must have extremely high resistance, as the current will split at a junction. If the voltmeter had low resistance, it would draw a lot of the current, and hence affect the current through the resistor whose voltage we seek to measure.

Question 7 Complete the following table and justify your choice. Connection

Resistance

Voltmeter

Parrallel

High

Ammeter

Series

Low

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 22 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

SUMMARY OF LESSON CLOSED, OPEN AND SHORT CIRCUITS •

An open circuit is one that is not complete, i.e. there is no connection between the two terminals. No current flows

•

A closed circuit is one which is connected to two terminals without a break in the circuit. Current flows through the wires.

•

A short circuit is created in a circuit where the current can take an alternate path (to the path with the resistor) that has little or no resistance. Current will flow entirely through the ‘short’ circuit and bypass the resistor.

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 23 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

SERIES CIRCUIT •

In a series circuit, resistors are connected consecutively, so that the current has only one path to flow

•

Voltage: The voltage drop across any resistor will be proportional to its resistance. ܸ = ‫ܴ × ܫ‬. Also, the sum the voltage drop across all resistors is equal to the supply voltage: ܸ௧௢௧௔௟ = ܸଵ + ܸଶ + ܸଷ …

•

Current: The current through all resistors is the same, since it only has one path to flow: ‫ܫ‬௡௘௧ = ‫ܫ‬ଵ = ‫ܫ‬ଶ = ‫ܫ‬ଷ …

•

Resistance: The net resistance of a series circuit is equal to the sum of the individual resistors – ܴ௧௢௧௔௟ = ܴଵ + ܴଶ + ܴଷ

•

Note that you need to calculate the net resistance before you can calculate the current and voltage

PARALLEL CIRCUIT •

When resistors are connected in parallel, the current has multiple pathways to flow

•

Voltage: the voltage across each of the resistors is the same: ܸଵ = ܸଶ = ܸଷ = ܸ

•

Current: since the current splits up, the sum of the currents across alternate paths is equal to the total current: ‫ܫ‬௧௢௧௔௟ = ‫ܫ‬ଵ + ‫ܫ‬ଶ + ‫ܫ‬ଷ

•

Resistance: The net resistance of the parallel circuit can be found by using

ଵ ோ೙೐೟

ଵ

ଵ

ଵ

=ோ +ோ +ோ భ

మ

య

AMMETERS AND VOLTMETERS •

Ammeters measure the current that passes through a resistor. They must therefore be connected in series (since the current through loads connected in series is the same). Ammeters must have low resistance, or it will reduce the current in the circuit and hence the resistor

•

Voltmeters measure the potential drop across a resistor, and must therefore be connected in parallel. A voltmeter must have very high resistance or it will draw the current from the resistor.

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 24 of 26

Headstart Phys&Chem

Electrical Energy III – Circuits

© TALENT 100

HEADSTART HOMEWORK 1. Complete the following table. The first box has been filled in for you.

Voltage

Current

Resistance

Series

Parrallel

2.

a) In the diagram above, show how you would connect a voltmeter and ammeter. b) Justify your choice in a) c) Identify the relative resistance of a voltmeter and ammeter and justify your choice.

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 25 of 26

Headstart Phys&Chem

© TALENT 100

Electrical Energy III – Circuits

3. Calculate the voltage, current through each of the resistors.

5ߗ

10ߗ

20ߗ

70V

4. Calculate the current and voltage through each of the resistors.

5ߗ

10ߗ

20ߗ

70V

TALENT 100: HSC SUCCESS. SIMPLIFIED.

www.talent-100.com.au Page 26 of 26