Activity: Simple circuits
In this activity you will come to understand how a simple cell creates potential difference. New terms (electromotive force and internal resistance) are added to existing vocabulary (potential difference) and you will be able sketch how terminal potential difference varies with time for a real battery. Ohm's law will be applied to a simple circuit and you will be able to derive an equation for electrical power.
Need to know
An electric cell is a device that converts chemical energy into electrical PE and a battery is made several of them joined together. What is basically happening is the atomic charges are being rearranged.
- Is there a difference in potential between points A and B in the mixed up atoms?
- Is there a difference in potential between A and B in the arranged charges?
- Explain why work has to be done to rearrange the charges.
- Can the arranged charges be used to do work on a + charge?
Have a look at this simulation:
- Notice how the electrons flow from the - to + side of the battery
- You can see how the electrons interact with the atomic lattice so that they drift through the conductor rather then accelerating.
- Why does work have to be done to take electrons from the + to - side of the battery.
- Where does the energy come from to move the electrons closer together?
- Click "show inside of battery" and all is revealed.
So fairies move the charges. This isn't really the answer but it might as well be as far as we are concerned in this course. If you want to know how chemical energy is converted to electrical PE in a battery you will have to study chemistry.
In this exercise Paul Falstad's circuit simulator will be used to simulate the simple circuits covered in the course. Note that the default symbol used for resistance is not the same as the one used by the IB, if you want the IB symbol choose "European resistors" from the options.
The simplest circuit consists of a cell and a resistor connected by wires.
- Open the circuit simulator and choose "blank circuit" from the "circuits" menu.
- Right click anywhere on the window and you will get a list of options. Select "voltage source 2 terminal" from the "inputs/outputs". The place it by click and drag.
- To change the properties of the component hover over it with the cursor (it will turn white), right click then choose edit from the list.
- Add a resistor and connect it to the battery with wires (all options in the right click list).
- To measure the properties of a component hover over it with the cursor, all details of that component will then appear
Equation for simplest circuit
Using the letters on the diagram answer the following:
- When a unit charge flows how much chemical energy is converted to electrical PE?
- According to Ohm's law what is the potential difference across the resistor?
- If energy is conserved we can say that ε = IR, explain why.
- Use the simulation to show this is the case.
Build the circuit below with a 5 V battery.
What is the PD across the 5 kΩ resistor?
V (4 sf)
Place your cursor on either side of the resistor and read the potential, PD is the difference.
3.621 - 0.001965
- Do the exercises on p 226
- Electric circuits multiple choice
Now know
For students with access to StudyIB:
Circuits 1