Electricity is like water! Revision: What is resistance and how does it affect the current? The water analogy

Aim The aim of the lesson is to be able to understand how the flow of electricity is similar to the flow of water.

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Question 9 or question 5 Explain what happens when you close the switch on a simple circuit. The battery always produces an electric field between its terminals. An electric field produces a force on charged particles – in this case the negative electrons in the wire. This force can be measured with the potential across the circuit. The potential pushes the electrons around the circuit. The number of electrons which go past a point every second is called the current. The current flowing through the bulb makes the bulb light up As soon as the switch is closed the current flows through every part of the circuit at the same time.

What do you remember? Answer on white boards. What is potential? What is potential measured in? What is current? What is current measured in? What is resistance? What is resistance measured in? What happens to the current if you increase the potential? What happens to the current if you increase the resistance? How can you calculate the current if you know the potential and current? Do light bulbs get brighter or dimmer if you add more bulbs to a (series) circuit? And why does that happen?

What do you remember? y_electricity_forces/electric_current_voltage/revi sion/1/

Pump Direction of water flow (10 litres) Water wheel The Water Model Direction of water flow (10 litres) Pipes

The Water Model

Answer the questions and then do the practical.

The Water Model - Analogies 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. The flow of water is like the current The water is like the charge (electrons). 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.

How would you increase the rate of flow ? Make the pump work faster or use a smaller water wheel. How would the speed of the water wheel change if there was more than one wheel in the pipe? It would get slower. What would happen to the water wheel if the rate of flow was increased? It would move faster. What happens to current when potential difference is increased. It goes up because the push on the electrons is higher. If you add another bulb in series in a circuit… the first bulb get dimmer because there is more resistance to the current. Using the model to make predictions

You can measure the resistance by using this circuit?

What have you learnt? You can compare the flow of electricity to the flow of water. The battery is like a _________ A bulb can be like a _____________ The pipes are like _____________ You can use this model to make predictions. Next week we‘ll use the model to design some circuits.