Voltage is an electrical pressure, which forces the electric charges (electrons) to move in an electrical circuit. Voltage is measured in volts, abbreviated as ‘V’. To understand the concept of voltage, consider a water pump which is pumping the water. The pump pushes the water to flow in the pipes. The pump acts like the voltage and the water acts like charges.

However, it is not necessary that when the voltage is applied, the electric charges will flow (current). Charges need a complete closed path to flow.


Electric current is the number of electrons flowing through a point in a circuit. Consider a circuit, which is marked ‘A’ at a point. The number of electrons that will pass through the point ‘A’ in one second will be the current of the circuit. You can consider the current in a circuit as a flow of water in the pipes.

The current in a circuit is caused by the voltage, much like the water flow in the pipes is caused by the pump. Electric current is measured in the amperes, sometimes called “amps”. It is denoted by the letter ‘I’.


Resistance, as the name suggests, provides the resistance to the electrical current. It always tries to stop the current from flowing. Every material around the world has resistance for electric current.

Some materials have very small resistance, called conductors. While, other materials have very high resistance, called insulators. We use the conductors in the circuit for electric current to pass easily.

Resistance depends on the structure of the material:

  • If a material has more free electrons like metals, it will act as a conductor.
  • If a material has fewer free electrons like rubber, it will act as an insulator.

Relationship between Voltage, Current, and Resistance

The relationship between voltage, current, and resistance can be found from the ohm’s law:

V = I*R  ;              Here,  V = Voltage, I = Current, R = Resistance

See the Ohm’s Law for further information.

AC and DC

There are two types of current that flow in a circuit. One is called DC (Direct Current) and other is AC (Alternating Current).

  • DC: Direct current is the flow of electrons in one direction. Although, the magnitude of the current can decrease or increase but it will always flow in one direction in a circuit. Batteries and charger produce the DC.
  • AC: Alternating current doesn’t flow in one direction in a circuit. Instead, it changes its polarity (direction) constantly. The rate of changing polarity is called the frequency of AC. We all use AC current in our homes with 50 to 60 Hertz frequency. AC is often converted into DC by the chargers to charge your laptop and smart phone’s battery.

Interesting Facts

  • If the voltage is sufficient enough, electric current can pass through air. Lightning strikes, when the voltage builds enough to pass through air.
  • When current pass through a conductor, it produces a magnetic field around it.
  • Voltage is measured by a voltmeter. Whereas, current is measured by the ammeter.

simple-electromagnetAn Electromagnet is the kind of magnet, which uses electric current to create a magnetic field. It can attract and magnetize ferromagnetic materials like Iron, Nickel, and Cobalt. It is easy to make a simple electromagnet at your home from household materials.

Things You Will Need

  • Thin Plastic insulated wire
  • 5 volt AA Battery
  • Iron Nail

How to Make

  1. Wrap 20 turns of insulated wire on an iron nail tightly
  2. Trim about an inch of plastic coating from both ends of the wire.
  3. Connect one end of the wire with the positive terminal of the battery, and other with negative terminal. Use the electric wire tape if necessary.
  4. Get some paper clips and bring your electromagnet near them. You will see the paper clips will be attracted towards your electromagnet.

Disconnect wires from the battery, if wire or battery gets hot.

How it Works

When you connect the wires to the battery, an electric current flows in the wires. This electric current produces the magnetic field around the wire. The iron nail acts as a magnetic core. Magnetic cores are used to enhance the magnetic field.

Try It

  • Try to use two 1.5 volts AA batteries, and connect them in series. Then, connect the wires to this battery and observe the effects. Find out, does it affects the strength of the electromagnet
  • Use thicker wire instead of thin wire, and wrap around the iron nail. Then, observe the strength of an electromagnet
  • Use thick iron nail or bolt. Then, observe does it affect the strength of an electromagnet.

Try above methods, and note down your result. In the end, you will find which method is affecting the strength of electromagnet most.