Answer:
L = 182.4 m
Explanation:
Given:-
- The number of turns of the coil, N = 50
- The shape of the coil = square
- The angle between the coil and magnetic field, θ = 30°
- The change in magnetic field, ΔB = ( 700 - 250 ) μT
- The time duration in which magnetic field changes, Δt = 0.3 s
- The induced emf, E = 60.0 mV
Solution:-
- The problem at hand is an application of Faraday's law. The law states that the induced emf ( E ) is proportional to the negative rate of change of magnetic flux ( ΔФ / Δt ) and number of turns of the coil ( N ).
- The Faraday's law is mathematically expressed as:
E = - N* ( ΔФ / Δt )
Where,
- The flux ( Ф ) through a current carrying with an cross-sectional area ( A ) at a normal angle ( θ ) to the direction of magnetic field ( B ) is given by the following relationship.
Ф = B*A*cos ( θ )
- We need the rate of change of magnetic flux ( ΔФ / Δt ) for the Faraday's law. I.e the induced emf ( E ) is proportional to rate of change in magnetic field ( ΔB / Δt ), rate of change of angle between the coil and magnetic field ( Δθ / Δt ) or rate of change of cross-sectional area of the coil under the influence of magnetic field.
- To determine the exact relationship. We will derive the multi-variable function of flux ( Ф ) with respect to time "t":
Ф ( B , A , θ ) = B*A*cos ( θ )
- The first derivative would be ( Use chain and product rules )
( ΔФ / Δt ) = ΔB / Δt*A*cos ( θ ) + B*ΔA/Δt*cos ( θ ) - B*A*sin ( θ )*Δθ/Δt
- For the given problem the only dependent parameter that is changing is magnetic field ( B ) with respect to time "t". Hence, ( ΔA/Δt = Δθ/Δt = 0 ):
ΔФ / Δt = (ΔB/Δt)*A*cos ( θ )
- Substitute the rate of change of magnetic flux ( ΔФ / Δt ) into the expression for Faraday's Law initially stated:
E = - N*(ΔB/Δt)*A*cos ( θ )
- Plug in the values and evaluate the Area of the square coil:
A = - E / ( N*(ΔB/Δt)*cos ( θ ) )
A = - 0.06 / ( 50*[ (250-700)*10^-6/0.3 ] *cos ( 30° ) )
A = - 0.06 / -0.07216
A = 0.8314 m^2
- The square coil has equal sides ( x ). The area of a square A is given by:
A = x^2
x = √0.8314
x = 0.912 m
- The perimeter length of a single coil in terms of side length "x" is given as:
P = 4x
Whereas for a coil of N turns the total length ( L ) would be:
L = N*P
L = 4Nx
L = 4 * 50 * 0.912
L = 182.4 m ... Answer
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