As per phenomenon of electromagnetic induction an emf is induced in a coil when a magnetic flux linked with it changes. It is possible that emf is induced in single isolated coil due to change of magnetic flux through the coil by means of varying the current passing through the same coil. This phenomenon is called 'self-induction'. If we have coil of N turns closely wound together and a current I is passed through the coil then total magnetic flux associated with it Nphi_(B)propto I or Nphi_(B) = LI ...... (1) Here phi_(B) = flux linked with each turn of a coil. The proportionality constant L is known the self-inductance of the coil and its value depends on the dimensions of the coil and nature of core material. If the current flowing through the coil changes then an induced emfe is set up as : varepsilon =-d/dt(Nphi_(B))=-L(dI)/dt ......(ii) (a) Define self-inductance of a coil in terms of induced emf. (b) Obtain SI unit of self inductance. (c) Write its dimensions. (d) Do you agree with the statement "Self-inductance is electromagnetic analogue of mass in mechanics" ? (e) Why do we see some spark in the switch of an electric fan when a running fan is switched off?

As per phenomenon of electromagnetic induction an emf is induced in a

1.	As per phenomenon of electromagnetic induction an emf is induced in a coil when a magnetic flux linked with it changes. It is possible that emf is induced in single isolated coil due to change of magnetic flux through the coil by means of varying the current passing through the same coil. This phenomenon is called 'self-induction'. If we have coil of N turns closely wound together and a current I is passed through the coil then total magnetic flux associated with it Nphi_(B)propto I or Nphi_(B) = LI ...... (1) Here phi_(B) = flux linked with each turn of a coil. The proportionality constant L is known the self-inductance of the coil and its value depends on the dimensions of the coil and nature of core material. If the current flowing through the coil changes then an induced emfe is set up as : varepsilon =-d/dt(Nphi_(B))=-L(dI)/dt ......(ii) (a) Define self-inductance of a coil in terms of induced emf. (b) Obtain SI unit of self inductance. (c) Write its dimensions. (d) Do you agree with the statement "Self-inductance is electromagnetic analogue of mass in mechanics" ? (e) Why do we see some spark in the switch of an electric fan when a running fan is switched off?
Answer» Solution :(a) As`varepsilon = -L (dI)/DT,` hence `\|varepsilon\| = L if (dI)/dt=1.` Hence self-inductance of a coil is defined as the magnitude of emf induced in it when current passing through the coil changes at a unit rate. (b) In the relation `lvarepsilonl = L (dI)/, If (dI)/dt = 1 As^(-1) and lvarepsilonl = 1V`, then L = 1 and it is called a henry (H). So, SI unit of inductance is that in which 1 volt emf is induced on changing the current flowing through it at a rate of 1 ampere per second. (d) Self-inductance is electromagnetic analogue of mass in mechanics because induced emf due to self-inductance opposes any change of current in a circuit by itself i.e., self-inductance plays the role of electrical inertia. (e)When a running electrical fan is switched off, current flowing in the circuit falls to zero and consequently an induced emf is produced across the switch. As a result, a LIGHT spark takes place in the AIR gap of switch.

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