Electricity UNIT 4 / 4.2 CURRENT VOLTAGE RESISTANCE CIRCUIT DIABRAMS SERIES and PARALLEL CIRCUIT Electricity

Circuit diagrams Lesson aims: To know and be able to draw basic circuit symbols. To be able to draw and build basic circuit diagrams.

Circuit Diagrams 1 On your WB, draw the correct circuit diagram symbol.

A cell

A wire

A bulb (light)

An open switch (circuit off)

An ammeter and voltmeter

WHY??? Do we use circuit diagrams?? EASIER, FASTER, EASILY RECOGNISEABLE…

Before we move on… Everyone stand up, walk around. By drawing in the air, try and get someone else in the class to guess a symbol. Teacher demonstration!

Circuit Diagrams 2 Each group needs: One switch A battery pack 2 bulbs An ammeter A voltmeter 5 wires Using the equipment, try to build the following circuits. Hands up when you are done (yes it is a RACE!!). One person from each group will go and check the other groups (when I say!).

Circuit 1

Circuit 2

Circuit 3

Circuit 4

Can you draw this circuit?

Now… Build a basic circuit using your equipment. Another group will come to your desk and try and draw that circuit.

Match the circuit symbols

Current diagrams Lesson aims: To know and be able to draw basic circuit symbols. To be able to draw and build basic circuit diagrams.

Understanding electric current Lesson aims: To know what electricity is. To be able to explain current and voltage.

What is an electrical circuit? An electrical circuit is like a central heating system: There is a pump that pushes water around the system. The water everywhere starts to move at the same time. There are pipes that carry the water. The water flows through the pipes.

What is an electrical circuit? Worksheet 1 accompanies this slide.

Summary sentence In your group (3 or 4), write a summary sentence, including the following language. ; ( Include equations with the symbols and units.) Current Push Battery Voltage Resistance Electric circuit (electricity = the flow/movement of electrons)

Choose the best/most complete. Walk around, choose which summary you think is the most complete. Draw a smiley face on the one you choose!

Summary sentence An electrical circuit carries current, which is the flow of electrons, pushed around wires by a battery, the strength of which (the push/potential energy difference) is called the voltage.

Understanding electric current Lesson aims: To know what electricity is. To be able to define current and voltage.

Series and parallel circuits Lesson aims: - To be able to recognise and build SERIES and PARALLEL circuits. - To know why we would use SERIES or PARALLEL circuits. - To know the differences in voltage and current for SERIES and PARALLEL circuits.

Build this circuit… 2 minutes! Ready…. GO!!!

Now Build this circuit… 2 minutes! Ready…. GO!!!

What is the difference? A B Which is SERIES, which is PARALLEL? We are now going to carry out various experiments on these circuits. Record each all the results in your NBs.

1. BULB brightness Create both circuits. Are the bulbs the same brightness as in the other circuit?

2. Circuit breaking What happens when you remove one of the bulbs in each of the circuits? SERIES = no current a only one pathway (no complete circuit) PARALLEL = the other bulb still lights up (there is a complete circuit) Why would this be useful?

3. Current in series and parallel You are going to measure the current at all the letter points in the 2 circuits  How do you think the current will change at each point? Consider a river and the flow of water… What would happen to the amount of water? Measure A, and then write a HYPOTHESIS for the remaining measurements…

3. Current in series and parallel RESULTS?? A = B Why? Current is the flow of electrons. This is not used up, it just keeps moving around… F = C = (D+E) At this point… The current splits (more current will flow through the EASIER route)

4. Voltage in series and parallel Measure the voltage across all the bulbs and record your results.

QUESTION RACE!!! Ready???

Investigating circuits Create a simple SERIES circuit with bulbs and power. Now draw this circuit in your book… Add more bulbs into the circuit, What happened? Describe your observation in your book (what you saw). The brightness of the light decreased! WHY?? Now increase the power from 6V to 9V The brightness of the light increased! Why??

INVESTIGATING CIRCUITS Now repeat the same experiments, but by adding more bulbs in PARALLEL… Write down your observations and reasoning.

Experiment 1: current in a series circuit

Current in a series circuit: summary

Measuring voltage Voltage is measured using a device called a voltmeter. In a circuit diagram, a voltmeter is given the symbol V. When measuring the voltage across a component, the voltmeter is always connected in parallel with (or across) the component. This is still a series circuit, as the voltmeter does not affect the circuit. The voltage supplied by the battery is shared between all the components in a series circuit.

Experiment 2: voltage in a series circuit

Voltage in a series circuit: summary

Measuring current in a parallel circuit Set up the circuit as shown. Place an ammeter, in turn, at positions 1, 2, 3 and 4 and record the readings in a table. Current (A) A1 A2 A3 A4 Ammeter

Current in a parallel circuit In a parallel circuit, the current that leaves the cell is the same as the current that returns to the cell. The ammeter readings for A1 and A4 should be the same. This is because the current does not get used up by the circuit, just the energy that the current is carrying.

Current in a parallel circuit The current splits up at the first junction and then joins together at the second junction. The following is always true for this type of parallel circuit: A1 = (A2 + A3) = A4 If the bulbs are identical, then the current will split evenly. If the bulbs are not identical, then the current will not split evenly.

Measuring voltage in a parallel circuit Connect up this circuit and measure, in turn, the voltage at V1, V2 and V3. Record your results in the table. Voltage (V) V1 V2 V3 Voltmeter What do you notice about the results? How can you explain this?

Make your own parallel circuit

Cells in a parallel circuit: summary

Series and parallel circuits: summary Worksheet 2 accompanies this slide. The worksheet involves a simple role play to model a circuit.