Target

To know how to set up a series circuit

Electricity

Thursday 9 February 2017

A circuit is like a central heating system in a house:

Boiler and pump

radiator

High pressurelow pressure

There is a pump that pushes water round the system. The water everywhere starts to move AT THE SAME TIME.

There are pipes that CARRY the water.

In the pipes the water is FLOWING.

flow ofwater

An electrical circuit is very similar to a central heating system.The bulb in the circuit is like a radiator. An electrical device uses electrical energy supplied by the circuit.

Instead of a flow of water, electricity flows in an electrical circuit. The wires are like pipes; they carry the electricity(called current) round the circuit.

The electrical current is pushed by the battery, which has the same function as the pump and boiler. The strength of push provided by the battery is called its voltage.

lamps

This is a simple series circuit. In a simple series circuit, everything is connected in one loop across the terminals of the battery. So there AREN’T any points where the current can split or join (these are called junctions).

This circuit has two lamps connected in series. Circuits are always drawn using straight lines.

Series circuit

Here are some other simple series circuits:

1. Two resistances (resistors) connected in series.

2. A rheostat (or variable resistor) and a bulb connected in series.

R1 R2

Series circuit

The unit of measure for current is the "amp" which has the symbol A.

We measure the current using a device called an ammeter. In a circuit this is given the symbol

When measuring the current through a component, the ammeter is always connected in series (in the same loop) with that component.

AA

A

Measuring current

When measuring the voltage across a component, the voltmeter is always connected in parallel with (or across) the component.

V3

V2

V1

We measure the voltage using a device called an voltmeter. In a circuit this is given the symbol V

The voltage supplied by the battery is shared between all the components in a series circuit.

This is still a SERIES circuit.

Measuring voltage

Series circuit

A

V

componenthere R

Voltage is measured by connecting the voltmeter across (or in parallel with) the component.

Voltage is measured in volts and the symbol for this is V.

V

Components

Measuring voltage - across a resistance or a bulb

1. Set up the circuit as shown above.2. Connect the voltmeter across the power supply and

measure the supply voltage. 3. Then connect the voltmeter across the resistance (R)

and measure this voltage.

Experiment: measuring voltage

R

V

V

Circuit 1

1. Add another resistance (R2) to the circuit as shown.2. Connect the voltmeter across the power supply and

measure the supply voltage. 3. Then measure the voltage across each of the resistances.

R1 R2

V

V1 V2

Circuit 2

Experiment: measuring voltage

Record your results:

Circuit 1: Voltage (supply) = V

Voltage (R1) = V

Circuit 2: Voltage (supply) = V

Voltage (R1) = V

Voltage (R2) = V

R1 R2

V

V1 V2

R1

V

V

Circuit 1 Circuit2

The current is the ____ of electricity around the circuit. The _______ is the amount of push.

When two components were put into Circuit 2, the voltage of the supply was the ____ as Circuit 1. However, the voltage across R1 ________ .

The voltage across both components in circuit 2 added to be equal to the _____ voltage.

supply, decreased, voltage, flow, same

Circuit2

R1 R2

V

V1 V2

R1

V

V

Circuit 1 Circuit2

V1

V2

V3

Measuring voltage in parallel circuits

Connect together the circuit shown above and measure, in turn, the voltage at V1, V2 and V3.

Write down your results in the table below :

Voltmeter Voltage(V)

V1

V2

V3

Explain anything you notice about the results.

Target

To know how to set up a parallel circuit

Electricity

Thursday, February 9, 2017

Parallel circuits

Parallel and series circuits

Experiment: measuring current

R1

1

2

A

1. Set up the circuit as shown above.

2. Measure the current using the ammeter at positions 1 and 2.

Circuit 1

A

R1 R2

1

2

3

A

A

A

1. Add another resistor into the circuit.

2. Now measure the current using the ammeter at positions 1, 2 and 3.

Circuit 2

Experiment: measuring current

Results

Current Position 1

Current Position 2

Current Position 3

Current Position 1

Current Position 2

Circuit 1

Circuit 2

Circuit 1

The current at different positions in the circuit, before and after the resistor, was the _____.Current is ___ used up by the components in the circuit.

Circuit 2

Increasing the number of components in the circuit _______ the current. The current at all points in a series circuit is the ____.

same / same / decreased / not

Conclusions

1. Set up the circuit as shown above.

2. Connect the voltmeter across the power supply and measure the supply voltage. Then measure the voltage across the resistance. Measure the current.

Experiment: cells

R1

V

V

Circuit 1

A

1. Add an additional battery to the circuit.

2. Connect the voltmeter across the power supply and measure the supply voltage. Then measure the voltage across the resistance. Measure the current.

R1

V

V

Circuit 2

A

Experiment: cells

Results

Circuit 1: one battery

Circuit 2: two batteries

Supply Voltage

Voltage R1

Current

Supply Voltage

Voltage R1

Current

Delete the wrong answer:

Increasing the number of batteries / cells increases/decreases the current that flows in the circuit.

The current/voltage depends on the current/voltage.

Conclusions

1. In a series circuit the current is the same at any point in the circuit.

2. The supply voltage is shared between the components in a series circuit.

3. The current depends on the voltage in ANY circuit.

Summary for series circuits

Parallel circuits

A parallel circuit is one which contains a point (a junction) where the current can SPLIT (point A) or JOIN (point B). This means that there is MORE than one path around the circuit.

A B

Measuring current in parallel circuits

A1

A2

A3

A41 2

3

4

1. Place the ammeter, in turn, at positions 1, 2, 3 and 4.

2. Record the ammeter reading at the points in the table shown.

Ammeter Current (A)

A1

A2

A3

A4

For a parallel circuit, the current that leaves the cell or battery is the same as the current that returns to the cell or battery. The current does NOT get used up by a circuit, just the energy the electrons are carrying.

A1 = A4

The current splits up at the first junction and then joins together at the second junction. If the bulbs are identical then the current will split evenly. If the bulbs are NOT identical, then the current will NOT split evenly. The following is always true for this circuit.

A1 = A2 + A3 =A4

Energy in circuits

This section deals with the energy transfers in electric circuits.

The most important thing to understand about energy is that it cannot be created or destroyed.

In all devices and machines, energy is transferred from one type to another.

lamps

When this circuit is connected, chemical energy stored in the battery is transferred via electrical energy to heat and light energy in the bulbs.

The total amount of heat and light energy is the same as the amount of chemical energy lost from the battery.

Energy transfer in electrical circuits

Notice, most of the energy from the battery does not produce light - most of it is wasted as heat!

chemical energy lost from battery (e.g. 100J)

heat energy of bulb 95 J transferred to

5J transferred to bulb aslight energy

Energy transfer in electrical circuits

Energy efficiency

We can work out the efficiency of an energy transfer:

x 100

For this bulb

efficiency = (5/100) x 100 = 5%

total energy input

useful energy output%Efficiency =

Other energy transfers

Batteries can power many things -

What sort of energy is the electrical energy transferred into in these examples?