Unit of Inductance: SI and CGS Units

Inductance is the ability of a current-carrying conductor or inductor to store the energy in the form of magnetic field. Henry is the unit of inductance and is denoted by ‘H’. An electromotive force is generated in a closed loop which is carrying current due to the inductance. 

Key Terms: Inductance, Inductor, Electromotive Force, Current, Magnetic field, Conductor, Closed loop, Electric circuit, Circuit, Voltage

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What is the SI Unit of Inductance?

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The SI unit of inductance is Henry (H).

• An electric circuit is said to have an inductance of 1 Henry when the current is changed at a rate of one ampere per second and this changing current produces a voltage of 1 volt in the circuit. 
• Henry is a derived unit that is based on 7 base SI units.
• The SI unit of inductance is Henry whereas the MKS inductance unit is Kg m² s^-2 A^-2.

1 Henry = 1 Kg m² s^-2A^-2

Other Inductance Units

Some other units of inductance are – 

• Some of the smaller units such as millihenry (mH) or micro-Henry are used to measure radio frequency and audio-frequency range. 
• Sometimes for a very high-frequency range, the nano-henry unit is also used to measure inductance.
• The unit Henry is basically used in case of high voltage.

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Inductance

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Inductance is the ratio of the voltage induced in a conductor to the rate of the change of the current causing the voltage induced. The inductance of a conductor depends on the geometry of a circuit. It is caused by the change in the magnetic field of the electric circuit due to the flow of electric current in the circuit. Inductance can also be referred to as the ability of a conductor to store energy in the form of a magnetic field.

L = \(\frac{\phi(i)}{i}\)

Here, L is inductance, (i) is the magnetic flux of current i and I refers to current.

Now, as \(ε = L{dI \over dt} ​ \)

\(L = ε{dt \over dI} ​ \)

\(L = {volt\ ×\ second \over ampere} ​ \)

Therefore, the unit of inductance is also equivalent to Volt-Second/Am

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Inductor

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Inductor is a passive device that stores or holds the energy in the form of a magnetic field. An inductor generally consists of a coil or a loop of a wire. As the inductance is directly proportional to the number of turns of the coil in the circuit. Hence, as the number of turns is increased, the inductance of the coil also increases. It is measured in Henry.

Inductor

Inductance of an inductor can be calculated by using the following formula:

L = \(\frac{Nx\phi}{i}\)

• where, L is inductance, 
• N refers to the number of turns in the coil 
• is magnetic flux and 
• i is the intensity of the current

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Working Principle of Inductor

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When an electric current flows through a conductor, it generates a magnetic field around it. 

• An inductor becomes an electromagnet, and the magnetic field of the inductor changes when the magnet is moved towards or away from that inductor. 
• Due to this, an electric current flows through the inductor which maintains the momentum and direction of the magnetic field. This is known as Electromagnetic Induction.
• When current flows, a magnetic field is generated or when that magnetic field is changed, the current flows. 
• The direct current is easy to pass but in the case of an alternating current, it gets difficult. 

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Factors Affecting Inductance

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The factors which affect the inductance in a circuit are:

• Location of the Coil: The inductance of a coil is directly proportional to the coil area. The larger the area of the coil, the inductance also increases.

• Coil Material: The inductance is greater if the magnetic permeability of the core around which the coil is wrapped is greater. If the magnetic permeability is less, then the inductance is less. 

• Coil Length: The inductance is inversely proportional to the length of the coil. The longer the length of the coil, the less inductance. If the length of the coil is shorter, the greater the inductance.

• ​Number of turns in a coil: If the coil is having a greater number of turns of the wire, the greater the inductance. If the turns are less, the inductance is less.

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Things to Remember

• The inductor is a passive device that is used to store or hold energy.
• The unit of Inductance is Henry
• The inductance of an inductor is dependent on the number of turns in the coil, the material of the coil, the length of the coil, and the area of the coil.
• The MKS unit of inductance is Kg m² s⁻² A⁻².
• The formula for inductance can be represented as L = \(\frac{\phi(i)}{i}\)

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Previous Year Questions

1. A 800 turn coil of effective area 0.05 m² is kept perpendicular to….[NEET 2019]
2. A cycle wheel of radius  0.5m is rotated with constant angular velocity of...[NEET 2019]
3. A long solenoid has 1000  turns. When a current of….[NEET 2016]
4. The average e.m.f. induced in the coil is 0.1 V, when it is removed from the field in t sec….[NEET 1991]
5. The current in a coil of L = 40 mH is to be increased uniformly from…..[VITEEE 2017]
6. A dynamo converts….[UPSEE 2014]
7. At the centre of the solenoid, a coil of  100  turns and radius  0.01 m  is….[NEET 2017]
8. In the series L−C−R circuit … [KCET 2011]
9. A rectangular coil of 100 turns … [KCET 2013]
10. A bar magnet is allowed to fall vertically … [KCET 2017]
11. Two identical coaxial coils P and Q  carrying equal amount of current in the same direction are ...[KEAM]
12. The polarity of induced emf is given by….[KEAM]
13. In a coil of resistance 100Ω , a current is induced by changing the magnetic flux through it….. [JEE Main 2017]
14. A jet plane of wing span  20m is travelling towards west … [KCET 2017]
15. A rectangular, a square, a circular and an elliptical loop, all in the...[NEET 2009]
16. A resistance 'R' draws power 'P' when connected to an AC source….[NEET 2015]
17. the region of magnetic field as shown in the figure below. Then the e.m.f. generated is….[NEET 2016]
18. A conducting loop in the shape of a right angled isosceles triangle of height...[JEE Advance 2016]
19. If a transformer of an audio amplifier has output impedance…..[JCECE]
20. the circular loop of wire is moved with velocity towards the infinite current carrying wire…… [VITEEE 2016]