Circuit symbols charge and current.pptx

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Circuit symbols, charge and current

Electricity

Lesson 1 of 10

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Warm-up

Electricity

Lesson 1 of 10

Answer each one, then check.

1

What is the unit of current?

2

What is the unit of time in physics calculations?

3

Which particles carry current in a metal wire?

4

What does a battery provide?

5

Convert 2 minutes to seconds.

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Warm-up - Answers

Electricity

Lesson 1 of 10

1

What is the unit of current?

The ampere (A)

2

What is the unit of time in physics calculations?

The second (s)

3

Which particles carry current in a metal wire?

Electrons

4

What does a battery provide?

A potential difference (a push for charge)

5

Convert 2 minutes to seconds.

120 s

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Learning Objectives

Electricity

Lesson 1 of 10

1

Draw and interpret circuit diagrams using standard symbols.

2

State that a source of potential difference is needed to make charge flow in a closed circuit.

3

Recall and apply Q = It.

4

State that the current has the same value at any point in a single closed loop.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Electricity

Lesson 1 of 10

CHARGE AND CURRENT

charge flow = current × time Q = It

Electric current is a flow of electrical charge. The size of the current is the rate of flow of charge. Charge is in coulombs (C), current in amperes (A) and time in seconds (s).

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Standard Circuit Symbols

Electricity

Lesson 1 of 10

Learn to draw these quickly and neatly.

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Drawing a Circuit Diagram

Electricity

Lesson 1 of 10

Use a ruler and standard symbols.

1

Start with the power supply

Draw a cell or battery.

2

Add components in series

Draw straight lines with square corners; no gaps.

3

Add the ammeter in series

It goes in the main loop where you want to measure current.

4

Add the voltmeter in parallel

It goes across the component you are measuring.

5

Check

Every component is joined by lines and the loop is closed.

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Charge Flow

Electricity

Lesson 1 of 10

A current of 3.0 A flows through a lamp for 20 s. Calculate the charge that flows.

1

Write the equation

Q = It

2

Substitute

Q = 3.0 × 20

3

Answer

Q = 60 C

ANSWER

60 coulombs

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Finding the Current

Electricity

Lesson 1 of 10

240 C of charge flows through a heater in 2 minutes. Calculate the current.

1

Convert the time

2 min = 120 s

2

Rearrange

I = Q ÷ t

3

Substitute

I = 240 ÷ 120

4

Answer

I = 2.0 A

ANSWER

2.0 A

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Key Ideas

Electricity

Lesson 1 of 10

Learn these.

A source of pd is needed

For charge to flow round a closed circuit there must be a source of potential difference, such as a cell.

Current in a series loop

The current has the same value at every point in a single closed loop.

Current is not used up

Charge keeps flowing round the loop; the components transfer energy from the charge.

Ammeter and voltmeter

Ammeter in series measures current. Voltmeter in parallel measures pd.

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Key Terms

Electricity

Lesson 1 of 10

Electric current

The rate of flow of electrical charge.

Charge

A property of matter that can be positive or negative; measured in coulombs.

Ampere

The unit of current; one coulomb per second.

Coulomb

The unit of charge.

Ammeter

Measures current; connected in series.

Potential difference

The energy transferred per unit of charge; measured in volts.

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Electricity

Lesson 1 of 10

YOUR TASK

Circuit Doodles

12 minutes

Draw circuit diagrams for: (a) a cell, a switch and a lamp in series; (b) the same circuit with an ammeter to measure the current in the lamp and a voltmeter to measure the pd across it.

1

Draw the loop with a ruler.

2

Add the meters in the right way.

WHAT A GOOD ANSWER SHOWS

(a) A loop containing a cell, closed switch and lamp. (b) The ammeter is in the loop (series); the voltmeter is drawn in parallel with the lamp only.

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Can I...?

Electricity

Lesson 1 of 10

Recognise standard circuit symbols.

Draw a series circuit.

Place an ammeter and voltmeter correctly.

Use Q = It.

Rearrange for current or time.

Convert minutes to seconds.

Explain why current is the same round a series loop.

State what is needed for charge to flow.

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Summary & Exam Focus

Q = It.

Symbols: cell, lamp, ammeter (A), voltmeter (V), and so on.

Ammeters in series, voltmeters in parallel.

Current is the same at every point in a series loop.

EXAM FOCUS

A current of 0.40 A flows for 30 s. Calculate the charge that flows. (2 marks)

Write the equation, substitute, and include the unit C.

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