answer of electromagnetic induction 1_09

8/11/2019 Answer of Electromagnetic Induction 1_09

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Physics

Suggested Solutions

Electromagnetic Induction 1

1.

State what is observed in the galvanometer when [4]

a. the magnet is moved towards the coil in the direction of the arrow marked;The needle of the galvanometer will deflect to the right.

b. the magnet is pulled away from the coil at the same speed;

The needle of the galvanometer will deflect to the left, to the same magnitude.

c. the number of turns in the coil is increased, with the magnet moving as in caseb!.

The deflection towards the left would be greater.

d. the magnet is held close to t he coil but not moving.

No deflection of needle.


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". horseshoe magnet copper wire

G

#he diagram shows an apparatus used to demonstrate electromagnetic induction. $length of copper wire is situated between the poles of a horseshoe magnet. #he ends

of a wire are connected to a centre%&ero galvanometer.

a. #he wire is now moved 'uickly in the direction indicated. #he pointer of the

galvanometer is observed to deflect momentarily to one side. (hy does this

deflection occur)

hen the wire is moved !uic"ly in the direction indicated, the wire

e#$eriences change in magnetic flu# lin"age, %1&

which sets u$ induced emf and current in the wire. %1&

b. *+plain why the deflection of the pointer is larger when

i. the magnet is stronger;

hen the magnet is stronger, there is greater magnetic flu# lin"age betweenthe $oles of the magnet. %1&

ii. the galvanometer is more sensitive.

hen the galvanometer is more sensitive, it will be able to detect smaller

units of induced current.


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c. State with a brief e+planation in each case, how the deflection observed would

have been different if the wire had been moved at the same speedi. in the opposite direction ["]

'eflection will be in the o$$osite direction. %1&

(hange of magnetic flu# lin"age e#$erienced by the wire is

reversed. %1&

ii. at right angle to the indicated direction, i.e. directly towards one of thepoles of the magnet.

No deflection observed. %1&

The wire does not e#$erience change in magnetic flu# lin"age as it moves

$arallel to the magnetic flu# lines. %1&


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. #he figure below shows two coils of copper wire would round a soft%iron rod. *ach

coil can slide easily on the rod. -oil is connected in series to a battery and a switchS. -oil / is connected to a sensitive centre%&ero meter. $s S is closed, a deflection is

seen on the meter for a short time0 during this time the coil slides apart a little.

Soft%iron

rod

P )

oS o

a. *+plain briefly why there is a deflection on the meter.

hen the switch is closed, magnetic field $roduced by the current in coil P

increases from *ero to ma#imum. %1&

(oil ) e#$eriences an increase in magnetic flu# lin"age as it is connected tocoil P by soft iron rod. +n induced emf and current is thus set u$ in coil ).

%1&

b. *+plain why the direction of the short%lived current that flows through the

galvanometer is from left to right when the S is closed.

sing right hand gri$ rule, the side of coil P nearer to coil ) is South $ole.

-ence, by len*s law, the side of coil ) nearer to coil ) will be induced with a

South Pole. %1&

-ence, using right hand gri$ rule, the induced current will be coming out of

the $a$er. %1&

c. n the figure, draw the magnetic field pattern set up in and aroundcoil whenthere is a current in coil .

d. State and e+plain what you would observe as S is opened.

/oth coils slide nearer to each otherThe galvanometer needle deflects to the left. %10 both $oints&

The change in magnetic flu# lin"age is reversed.

decreases from ma#imum to *ero2. %1&

N S


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e. (hat would be the effect on the change you have described in a! if the soft%iron

rod were removed and a wooded rod put in its place)

Needle of galvanometer will be deflected to a lesser e#tent.

answer of electromagnetic induction 1_09

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