Feb 2021

Magnetic Effect Of Currents & Force On A Wire In D.C. Motors

February 3, 2021

Electricity and magnetism used to be considered two different topics until the 19th century. Today, electromagnetism is a bourgeoning field in physics that studies electromagnetic forces that occur between electrically charged particles.

Electromagnets consist of coils of wire with electricity passing through them. We use electromagnets in many of our electrical devices such as generators, speakers, and MRI machines. As electricity flows through the wire coils, it creates magnetism. Hence, they are extremely useful as we can control the flow of electricity to turn the magnet on and off by completing or interrupting the circuit. Here, you will be able to understand more about the topic of electromagnetism. Let’s get started!

Magnetic effect of a current

The magnetic effect of an electric current is also known as electromagnetic effect. A current-carrying conductor, such as a wire, produces a magnetic field around it. The magnetic field lines are in concentric circles.

The direction of the magnetic field can be found by using the right-hand grip rule.

When the thumb is pointing at the direction of the current, the remaining fingers will curl in the direction of the field.

Force on current-carrying conductor

When you place the same current-carrying wire in another magnetic field, the wire will experience a magnetic force. This force is caused by the interaction between the two magnetic fields.

The direction of this force can be found using the Fleming’s left-hand rule.

Stretch the thumb, forefinger, and middle finger of your left hand such that all 3 fingers are perpendicular to each other. The forefinger points along the magnetic field lines, from north to south. The middle finger will point along the direction of the current, from positive to negative. Lastly, the thumb will show you the direction of the force.

The strength of the force can be increased by increasing the current or using a stronger magnet. Similarly, the direction of the force can be controlled by reversing the direction of the current or the magnetic field.

Magnetic field pattern of a solenoid

A solenoid is a long wire coiled up into a spiral shape. When an electric current flows through it, the magnetic field generated by the solenoid resembles that of a bar magnet. The field inside a solenoid is strong and uniform because of the current flowing within each coil. You can apply the right-hand grip rule here to determine the poles.

D.C. motor

D.C. motors can be found in objects powering your everyday life. From electric toothbrushes to personal mobility devices and lifts, D.C. motors are the muscles of the machine. Next, let’s explore the magnetic effects of currents and apply it when considering the force on a current-carrying conductor that drives D.C. motors.

A simple D.C. motor consists of a solenoid in a uniform magnetic field. When there is current in the coil, the magnet will exert a turning effect on the coil, causing it to rotate. The D.C. motor makes use of the turning effect in the current-carrying conductor (coil) to convert electrical energy into mechanical energy. This mechanical energy is released in the form of rotation to move your load.

The turning effect of the coil can be increased by increasing the electrical current or through the use of stronger or larger magnets. For example, increasing the number of turns on the coil can increase the nett turning effect. This is because each length of wire experiences an upward force; thus, doubling the wire can double the force.


Next time you hear the doorbell ring, take an elevator, or use an induction cooker, perhaps you might think about what you have learnt today! Physics is all about learning how the universe works – that’s what makes it so interesting!

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