Is this correct? If not can someone please help me, I\'m really having understan

Question

Is this correct? If not can someone please help me, I'm really having understanding how to determine the directions of everything, whether it is positive or negative, and why does the way the coil wraps around in #1 and #4 have any effect? (I attached the original photo to show what they looked like without writing)

4. Use Lenz's law to determine whether the induced current in the resistor R is from A to B or from B to A in the 4 configurations in Fig. 3. You should label the direction ofB the sign of AD /AM, the direction of B and the direction of 1 in the coil and R for each of the 4 cases. (4) N nduced induced A Insured Brnauked Figure 3 Four configurations A A A megahve nega hve po Sihve hve

Explanation / Answer

first of all the main difference between #1 and #4 is the orientation of coil

first understand the basics of magnets

from N pole flux comes out forms a closed path and enters back via S pole

now answer direction of Bsource ( the direction of B is same as that of flux)

if the S pole is near to the coil , the flux should enter into the S pole that should pass through the coil

so the direction will be from B to A for #1 , #2 and #4.

in #3 the N pole is near to coil so flux should leave from coil which should pass through the coil

so the direction will be A to B for #3.

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Now based on the movement of the magnet bar we are increasing or decreasing the amount of flux entering or leaving the coil.

if the magnet bar is moving in the direction of coil , flux is increasing therefore for

#1 , #3 and #4 the answer for sign of (delta phi)/(delta t) is +ve and that for #2 is -ve.

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Now comes the best part .

according to Faraday's law of induction when there is a change in magnetic field associated with a coil then their will be an induced field which will oppose the change which caused it. ( see for statements of faraday and lenz laws)

as we seen in #1

source magnetic field direction is from B to A and it is increasing.

if it wasn't changing their won't be an induced field. since it increasing the induced field should reduce it.

this can only happen if the induced magnetic field direction is from A to B.

now how to get the induced magnetic field in A to B direction.

first change in magnetic field induces an EMF which will produce a current which in return forms a magnetic field.

so if we know RH rule for finding magnetic field direction we can get it.

curl the fingers of right hand in the direction of current in coil, the thumb indicates direction of magnetic field.

so inorder to get induced magnetic field direction from A to B the direction of current will be A to B.

#4 has everything same as that of #1

ie., Source magnetic field from B to A and it is increasing

so as to oppose the change the induced magnetic field has to be from A to B.

the only difference is in orientation of coil which will affect the RH rule in getting the direction of current

here the current direction will be form B to A.

#2 Source Magnetic field from B to A and it is decreasing

so to oppose the change the induced magnetic field must in the direction of B to A.

so as per RH rule current direction will be B to A

#3 Source magnetic field from A to B and it is increasing

induced magnetic field direction has to be in the direction B to A

asper RH rule diretion of current will be in B to A.

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