coulomb of charge (electrons) think of it as a “bag of electrons” (containing...

Coulomb of charge (electrons)

Think of it as a “bag of electrons” (containing 6000000000000000000 electrons!)

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Current

The number of Coulombs flowing past a point in the circuit every second.

I = Q/t

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A

I’m counting how many

coulombs of electrons go

past me every second

1 Amp = 1 coulomb per second

In a series circuit

Current is the same at any point in the circuit

2.5 A

2.5 A 2.5 A

2.5 A

In a parallel circuit

The current splits (total current stays the same)

2.5 A

2.5 A

1.25 A

1.25 A

Voltage(emf)☺

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I’m checking the difference in energy (per

coulomb) between the 2 red arrows

1 Volt = 1 Joule per coulomb

Voltage (p.d.)☺

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V

I’m checking the difference in energy (per

coulomb) before and after the lamp

1 Volt = 1 Joule per coulomb

In a series circuitThe sum of the voltages across the lamps

equals the voltage across the cells

9 V

3 V 3 V 3 V

In a parallel circuitIn a simple parallel circuit, voltage across each lamp equals the voltage across the cells

5 V

5 V

5 V

Resistance

Measures how difficult it is for current to flow. Measured in Ohms (Ω)

VA

Resistance = voltage/current R = V/I

Resistance of a lamp

AV

Resistance = voltage/current R = V/I

Vary the voltage and current using a variable resistor (rheostat). Plot a graph of resistance against current

Resistance of a lamp

V(V) I(A) R(Ω)

I(A)

R(Ω)

Resistance of a lamp

• As the current in a lamp increases, it gets hotter, and its resistance increases. Why?

Ohm’s Law

• V = IR

V

RI X

Power

The amount of energy used by a device per second, measured in Watts (Joules per second)

VA

Power = voltage x current P = VI

Power

The amount of energy used by a device per second, measured in Watts (Joules per second)

VA

Power = voltage x current P = VI

☺Can you copy this please?

Example

• A 200 W television is plugged into the 110V mains. What is the current in the television?

PIV X

Example

• A 200 W television is plugged into the 110V mains. What is the current in the television?

• I = P/V = 200/110 = 1.8A

PIV X

Example

• A kettle uses 240V and 8A. What is its power?

PIV X

Example

• A kettle uses 240V and 8A. What is its power?

• P = VI = 240x8 = 1920W (=1.9kW)

PIV X

Electric symbols

Cell and battery of cells

Lamp

Switch

Ammeter

Voltmeter

Resistor

Variable resistor (rheostat)

Thermistor

• Resistance decreases with increasing temperature

Temp

Resistance

Light-dependent resistor (LDR)

• High resistance in the dark but a low resistance in light

Diode

• Allows current to flow in one direction only (from + to – in the direction of the “arrow)

Captain Jack Sparrow smoking a cigar

Two cowboys on a tandem

Two fried eggs in a frying pan

3 wizards looking down a well

Let’s try some MORE questions!