Current electricity

At the flick of a switch, turn of a knob or the push of a button, we have instant power. This is possible because of the electric current. Electric current has revolutionised modern-day living. From the time we wake up till the time we sleep at night, our life is dependent on electricity. From the basic bread toaster and baking oven to the commonly used television all require electric current to operate. The most common device, mobile phones, uses the electric current to charge the battery for operation. Besides playing a major part at home, electricity also plays an important role in industries, transportation, and communication. 

Electric current

When a lot of free electrons are all moving in the same direction, we call it an electric current. The amount of electric current refers to the number of electrons passing through an area per unit of time and is measured in amperes (usually called amps for short), abbreviated with a capital A. 

Electric Current is the rate of flow of electrons in a conductor. 

When electric charges move in a wire, we say that an electric current flows in the wire. It's like the way a current of water flows in a river. It is important to note that current does not get used up in a circuit.  

Batteries are often used as a source of electric current. A battery has a positive terminal, marked by a "+" symbol, and a negative terminal. The negative terminal has excess electrons, giving it a net negative charge. These electrons flow from the negative terminal to the positive terminal when there is a conductive path connecting them. 

The direction of conventional current is opposite this, from the positive terminal to the negative terminal, as shown in Figure 1.

Figure 1: When conductive material connects the two terminals of a battery, electrons will flow from the negative to the positive terminal. The conventional current will point from the positive to the negative terminal.

Conventional Current Flow: The conventional current flow is from the positive to the negative terminal and indicates the direction in which positive charges would flow.

Electron Flow: The electron flow is from negative to positive terminal. Electrons are negatively charged and are therefore attracted to the positive terminal as unlike charges attract.

For an electric current to flow, we need two things:

• something to make the electricity flow, such as a battery or power pack

• a complete circuit for the current to flow in

A circuit is made up of wires and components with a power source where current can flow, and the components will do work.

A simple circuit is where a bulb is connected to a power source so the bulb can give off light. This is called a simple series circuit.

Figure 2: This is a simple series circuit with 3 bulbs. 

Properties of the electric current

We know that electric current is the result of the flow of electrons. The work done in moving the electron stream is known as electrical energy. Electrical energy can be converted into other forms of energy such as heat energy and light energy. For example, the electric energy in a bulb is converted into light energy, electrical energy in an iron is converted into thermal energy. 

There are two types of electric current known as alternating current (AC) and direct current (DC). The direct current can flow only in one direction, whereas the alternating direction flows in two directions. Direct current is seldom used as an energy source. It is mostly used in low voltage applications such as charging batteries. 

Alternating current is used to operate appliances for household, industrial and commercial use.

The electric current is measured in ampere. One ampere of current represents one coulomb of electric charge moving past a specific point in one second.

1 ampere = 1 coulomb / 1 second

Current investigation

1. Click on the link below:

https://phet.colorado.edu/sims/html/circuit-construction-kit-ac-virtual-lab/latest/circuit-construction-kit-ac-virtual-lab_en.html

2.  Using the components on the left-hand side of the screen build a series circuit with:

1 battery

1 bulb

1 switch

3 ammeters

as shown in the picture below.

What do you notice about the current readings on the ammeters?

3. Copy this table into your notebook:

4. Using the Phet simulation build the following circuits, noting the brightness of the bulbs in your table. (Each time you need to add a cell, add a battery)

Whilst you are adding bulbs and batteries to your circuit, observe the speed of the animated electrons. 

What is the link between the brightness and the number of cells?  

What is the link between the brightness and the number of bulbs?  

Conclusion:

With 1 battery and 1 bulb, 2 batteries and 2 bulbs, 3 batteries and 3 bulbs, the brightness of the bulb(s) is/are normal.  

Adding cells/batteries to the circuit increases the brightness of the bulbs. This is because every time you add a battery, you give the current a bigger push to travel around the circuit. This causes an increase in the brightness.  

When you add any component to a circuit, they resist the current - they slow the current down. This causes the bulbs to be dim.  

The more components, the higher the resistance, the slower the current and the bulbs will be dim.

The more batteries, the faster the current, the brighter the bulbs will be.