Moving Charges and Magnetism Test

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Moving Charges and Magnetism Test - 27

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Weekly Quiz Competition

Question 1
1 / -0

In a moving cell galvanometer, we use a radial magnetic field so that the galvanometer scale is

A
logarithmic

B
exponential

C
linear

D
none of the above

Solution

In a moving cell galvanometer, we use a radial magnetic field so that the galvanometer scale is linear.
Question 2
1 / -0

A proton enters a perpendicular magnetic field of 20 Tesla. If the velocity of proton is $$4 \times 10^7 m/s$$ then the force acting on it will be :

A
1.28 Newton

B
$$1.28 \times 10^{-11} $$ Newton

C
12.8 Newton

D
$$12.8 \times 10^{-11} $$ Newton

Solution

$$F = qVB$$
so we have $$ B = 20 Tesla$$ and $$V = 4 \times 10^{7}$$
So putting this value
$$ Force = (1.6 \times 10^{-19})(20)(4 \times 10^{7})$$
$$ Force = 12.8 \times 10^{-11}$$ N
Question 3
1 / -0

An electron moving to the east in a horizontal plane is deflected towards south by a magnetic field. The direction of this magnetic field is

A
Towards north

B
Towards west

C
Downwards

D
Upwards

Solution

Answer is C.

An electron moving to the east in a horizontal plane is deflected towards south by a magnetic field. When the direction of the electron is from west to east, the current is in the reverse direction. That is, the current is in the east-west direction. Applying the right-hand thumb rule, we get that the direction of magnetic field at a point below the wire is from north to south. That is, downwards.
Question 4
1 / -0

A charge q is moving with a velocity v parallel to a magnetic field B. Force on the charge due to magnetic field is

A
q v B

B
q B/v

C
zero

D
B v/q

Solution

$$F_n = q (\vec v \times \vec B)$$
$$= qvB sin \theta$$
$$= 0$$ (because $$\theta = 0^o$$)
Question 5
1 / -0

The path of a charged particle moving in a uniform steady magnetic field cannot be a :

A
straight line

B
circle

C
parabola

D
none of these

Solution

Case 1 : If B is parallel to V $$\Rightarrow$$ in this case $$F_B=0 \Rightarrow$$ particle will move in a straight line.
Case 2 : If B is Perpendicular to V $$\Rightarrow$$ in this case $$F_B$$ is not equals to 0 and always pointed towards a fixed point.$$\Rightarrow$$ in this case particle will move in a circle.
Case 3 : If B is at some angle $${\theta}$$ with V $$\Rightarrow$$ in this case particle will move on a Helical path.
Except these 3 cases there is no such a case in which path of this particle will be a parabola.
Question 6
1 / -0

A conducting rod AB moves parallel to X-axis in a uniform magnetic field, pointing in the positive X-direction. The end A of the rod gets

A
positively charged

B
negatively charged

C
neutral

D
first positively charged and then negatively charged

Solution

According to right hand palm rule, the Lorentz force on free electrons in the conductor will be directed towards end B. Hence, the end A gets positively charged.
Question 7
1 / -0

What name is given to a cylindrical coil of diameter less than its length ?

A
Lactometer

B
Barometer

C
Bolenoid

D
Solenoid

Solution

A solenoid is a long coil containing a large number of close turns of insulated copper wire wound on a conducting or non-conducting material. The diameter of each of the circular coil is less than the total length formed by several circular coil wound on a soft iron core.
Question 8
1 / -0

A charged particle moves through a magnetic field in a direction perpendicular to it. Then the

A
velocity remains unchanged

B
speed of the particle remains unchanged

C
direction of the particle remains unchanged

D
acceleration remains unchanged

Solution

Magnetic force acts perpendicular to the velocity.
Hence speed remains constant.
Question 9
1 / -0

If electron velocity is $$2\hat{i} + 3\hat{j}$$ and it is subjected to magnetic field of $$4\hat{k},$$ then its

A
speed will change

B
path will change

C
both (a) and (b)

D
none of these

Solution

since magnetic field is perpendicular to the direction of option or the velocity vector of the electron. therefore, the force will always act perpendicular to the both direction of magnetic field as well as velocity vector of electron and electron will do a circular motion since magnetic field is uniform.
Hence only direction of motion will change.
Question 10
1 / -0

Two free parallel wires carrying currents in the opposite directions

A
attract each other

B
repel each other

C
do not affect each other

D
get rotated to be perpendicular to each other

Solution

Let wire on RHS carry current vertically upwards and wire on LHS carries current vertically downwards then the direction of magnetic field at a postion where RHS wire is there due to LHS wire is out of the plane. Now RHS wire is a current carrying conductor placed in a magnetic field due to LHS wire. Similarly LHS wire is a current carrying conductor placed in a magnetic field due to RHS wire. Therefore, they both will experience force.
Now in RHS wire current is vertically upwards and direction of magnetic field is out of the plane. Since direction of force is given by $$F=\overrightarrow {dl}\times \overrightarrow B$$ therefore, force acting on RHS wire is towards right and by applying similar method we find that force acting on LHS wire is towards left. Therefore, they both repel each other.

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Moving Charges and Magnetism Test - 27

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Moving Charges and Magnetism Test - 27

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Question 1

logarithmic

exponential

linear

none of the above

Solution

Question 2

1.28 Newton

$$1.28 \times 10^{-11} $$ Newton

12.8 Newton

$$12.8 \times 10^{-11} $$ Newton

Solution

Question 3

Towards north

Towards west

Downwards

Upwards

Solution

Question 4

q v B

q B/v

zero

B v/q

Solution

Question 5

straight line

circle

parabola

none of these

Solution

Question 6

positively charged

negatively charged

neutral

first positively charged and then negatively charged

Solution

Question 7

Lactometer

Barometer

Bolenoid

Solenoid

Solution

Question 8

velocity remains unchanged

speed of the particle remains unchanged

direction of the particle remains unchanged

acceleration remains unchanged

Solution

Question 9

speed will change

path will change

both (a) and (b)

none of these

Solution

Question 10

attract each other

repel each other

do not affect each other

get rotated to be perpendicular to each other

Solution

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