Expectations - Ms Holland's Physics Site

Expectations - Ms Holland's Physics Site

Electric Fields and Current Complete the atoms worksheet as your starter. You need your Periodic Table from last lesson! Recap Questions 1. What particle carries negative Electron & Proton

charge and what particle carries positive charge? 2. When two materials are rubbed together, what type of Electrons particle is transferred?

Describe this persons hair Can you explain what is happening here? What is current? Current is the rate of flow of charge. It is measured in amps (A) and has the symbol I.

How do we measure current in a circuit? You can measure current in a circuit using an ammeter. Current analogy Electrical current is like current in a river. We

can say that the current in a river can be calculated as, So the equation for electrical current would be, Voltage

1V 1J e Weve got all this energy! Lets go and give it to a bulb, or a motor, or something!

e e e e The Coulomb Gang 2V 1J 1J e

e e e e This battery gives us twice as much! Fixed Voltage Cell A cell is a fixed-voltage device. It has its voltage written on it. The cell will always give the same number of joules to each coulomb coming through. A 5 V battery will always give 5 J to

every coulomb of electrons. Somehow it is always able to keep up. Even if the coulombs are coming through thick and fast (high current), it will still manage to give 5 J to every coulomb passing through. Fixed Voltage Cell electrons all start moving at once when switch is closed

We always refer to the voltage across a component (not through it). The voltmeter tells you the difference between the joules per coulomb going into the component and the joules per coulomb coming out. Conservation of energy All the joules given by the battery to the electrons are exactly used up by the time the electrons get back to the

battery. Question: Youve already seen that you can get different currents with the same battery, depending on what you connect to it. What difference will the size of the current make to the lifetime of the battery? Conservation of energy The Coulomb Gang all out of energy

e 2V 1 J1 J e e e e e e e e

e V This battery is giving 2 J to every coulomb of electrons passing through. The voltage is (+)2 V.

Conservation of energy 1J 1J 1J e e e e e

e e e e e V This bulb is taking 1 J from every coulomb of electrons passing through.

The voltage is (-)1 V. Simple Series Circuit Direction of electric current (10A) Cell Direction of electric current (10A)

Wires Bulb The Water Model Direction of water flow (10 litres) Pump

Pum p Pipes Water wheel Direction of water flow (10

litres) The Water Model Pump The Water Model Pump

The Water Model Pump The Water Model Pump The Water Model

Pump The Water Model Pump The Water Model Pump

The Water Model Pump The Water Model Pump The Water Model - Analogies The water is like the charge (electrons).

The flow of water is like the current. The pipes are like the wires. The pump is like the cell (or battery) because it provides the push for the water. The water carries kinetic (movement) energy just like current carries electrical energy. The water wheel is like the bulb as the energy from the water is used to turn the water wheel like the electrical energy is used to light

a bulb. Using the model to make predictions: 1.How would you increase the rate of flow (how fast the water was moving)? 2.Explain how the speed of water wheels would change if there was more than one wheel in the pipe. 3.What would happen to the water wheel if the rate of flow was increased?

Now explain: 4.What happens to current when potential difference is increased. 5.What happens to the brightness of bulbs if more than one is placed in series. 6.Why energy increases when potential difference increases. Adding Branches Parallel Circuits 5 Amps 10

Amps 5 Amps 10 Amps Adding Branches - Parallel Circuits 5 litres 10 litres 5 litres

Pump 10 litres What are the limitations? The water model has some limitations: It cannot explain short circuits the water would flow wherever a branch was situated. If a pipe was cut then the water would flow out, but some would remain in the pipe to turn the wheel. If a

wire is cut in a circuit then the bulb will immediately go out.

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