To start, we need to define current and voltage:
- Current is the rate (or speed) at which the electrons are flowing through the circuit and is measured in amperes (Amps).
- Voltage is technically the electrical potential difference between the beginning and end of a circuit….or simply, the force at which the current travels through the circuit. Voltage is measured in Volts (joules/coulomb).
We are going to start with the simple circuit we created in a previous post (connect the alligator clip to negative side of battery, then connect to knife switch, knife switch to lamp holder, lamp holder to positive side of battery).
Now let’s make some modifications and create a parallel circuit. In a parallel circuit, the voltage stays constant in each branch of the circuit.
Creating a Parallel Circuit
Using our simple circuit with the knife switch in the upright position, we are going to add another load (light) and create a parallel circuit.
- Take a wire with alligator clips and attach to one side of the existing lamp holder.
- Using a separate wire, attach one end to the other side of the existing lamp holder (*note: there will be 2 clips attached to each side of the existing lamp holder).
- Take the ends of the two wires that are free and clip one to each side of a new lamp holder with light bulb. When the knife switch is closed, both lights illuminate.
In a parallel circuit, the voltage stays constant in each branch of the circuit. So, using a 1.5V battery, both bulbs are receiving 1.5V of electricity. This is the reason both light bulbs have the same brightness. If you measured the current, you will find that the current is divided into each branch. Therefore, if 10 amps of current were flowing through the circuit, each light (or branch of the parallel circuit) would be receiving 5 amps of electricity. Adding the amount of current in each branch together, will give the total amount of current introduced into the circuit.
Now you’re well equipped to teach your students all about parallel circuits. Amazon has a many experiments to teach and explain how circuits work. Check out Energy Ball and Energy Stick.
Teaching circuits to students
Electricity can be a complex and imposing topic to present to your students. Before we talk about circuits, let’s go over a few definitions:
- Load – A device that does work or performs a job (i.e., the light bulb in our circuit).
- Electrical current – The flow of electrons from an area of high concentration (“a lot”) to an area of lower concentration. *Note: the negative side of the battery has a high concentration of electrons.
- Electron –Â A negatively charged particle that orbits the nucleus of an atom.
- Generator – A device that converts mechanical or chemical energy into electricity. Wind, water or an engine can power a generator.
- Electrical circuit – An electrical path that is closed (all parts connected), allowing the electricity to return to the original source (the battery).
- Parallel Circuit – A circuit in which the components are connected like a ladder. This circuit splits the voltage equally to all of the components.
Creating a Simple Circuit
- Place a “D” cell battery in a battery holder. The battery holder will allow you to attach wires with alligator clips to the positive and negative ends of the battery.
- Now, screw a small light bulb (mini lamp) into a lamp holder. Like the battery holder, the lamp holder will allow you to attach alligator clips to the light bulb (your load).
- To complete the circuit, you will need two wires with alligator clips. Use one wire to connect the negative side of the battery to the lamp holder. It does not matter which side of the lamp holder the wire is attached. Connect the positive side of the battery to the lamp holder using the second wire. This wire will attach to the opposite side of the lamp holder. The light bulb should be lit.
Remember, the voltage of the battery and light bulb should be similar. If the battery voltage is too much larger than the voltage capacity of your bulb, the bulb will burn out. A “D” cell battery provides 1.5V.
Simple Circuit with Switch
Adding a Knife Switch to a Simple Circuit
We will modify our simple circuit described above to complete this task.
- Disconnect the alligator clip that is attached to the negative side of the battery and re-connect it to one side of the knife switch. Make sure the knife switch is in the upright position.
- Take a separate wire and connect the negative side of the battery to the knife switch. Notice that the light is off.
- Lower the arm on the knife switch to connect the circuit and light the bulb.
The knife switch allows you to discuss breaking the circuit and stopping the flow of electrons.
Heath Scientific provides a kit called “Making Circuits Simple” that includes all of the components described in this article. It’s an easy, all-in-one kit to demonstrate circuits to your students.
Sodium Bicarbonate, Calcium Chloride and Phenol Red
Let’s go over the procedure first and then we will discuss what is happening.
1. In a quart baggie, place sodium bicarbonate(1 tsp) in one corner and calcium chloride(1 tsp) in the other.
2. Lay the bag on its side and place a small cup (medicine cup size – 1 oz) of phenol red in center of the bag. Be careful not allow the any on the chemicals to mix yet. Seal the bag
3. Gently pour the phenol red where it spills into each corner. Do not mix the two corners yet.
4. Have the students feel each corner and make observations. Continue the observations for a few minutes.
5. Pick the bag up and gently move the bage side to side, mixing the chemicals. What happens?
The side of the bag with calcium chloride becomes warm. The calcium chloride dissolves forming calcium and chloride ions. The release of heat (exothermic) is a result of the calcium chloride dissolving and not a chemical reaction.
When the sodium bicarbonate dissolves to form sodium, hydrogen and carbonate. It becomes cool (endothermic). The baking soda absorbs heat in order to dissolve. This is not a chemical change.
When the two sides are mixed, calcium carbonate is formed which is insoluble. Also formed are water and carbon dioxide. The carbon dioxide (gas) causes the bag to inflate. When the carbon dioxide dissolves in the liquid, carbonic acid is formed. This change in pH causes the phenol red to turn yellow. A chemical change has now occurred.
Remember to have the students use all lab safety measures. If the bag becomes over inflated, release some of the gas.