Question

A rod PQ is connected to the capacitor plates. The rod is placed in a magnetic field $\left( \overrightarrow{B} \right)$ directed downward perpendicular to the plane of the paper. If the rod is pulled out of a magnetic field with velocity $\overrightarrow{v}$ a shown in figure.

A. Plate M will be positively charged.
B. Plate N will be positively charged.
C. Both plates will be similarly charged.
D. No charge will be collected on the plates.

Answer 1

According to faraday's law, whenever there is a change in magnetic flux, an emf will be induced in the loop. So, while moving the rod PQ, a potential will be developed inside the loop and the capacitor plates will get charged. We will find the direction of current with help of Fleming’s right hand rule.

Complete step by step answer:
Before solving the question, let us understand what Fleming’s right hand rule is. It shows the direction of induced current when a conductor attached to a circuit moves through a magnetic field.
According to Fleming’s right hand rule,
The thumb points the direction of movement of the conductor.
The first finger/Forefinger represents the direction of the magnetic field.
And the second finger represents the direction of induced current.
That is,

Now, if we apply Fleming’s right hand rule for the given question, we can see that the current will be induced upwards through the conductor. i.e.

So, we know that current is flowing upwards through the conductor. Now, we will draw an equivalent circuit and find out which plate will be charged positive and which one will be negative.
We must also know that the flow of electrons will be opposite to the direction of current.

So, from this, we can understand that positive charges will be moving towards plate M and electrons move towards plate N.
Therefore, plate M will be positively charged and plate N will be negatively charged. So, option A is correct.

Note:
While solving these types of questions, don’t get confused over Fleming’s rule whether right hand or left hand rule is used to find the direction. If we need to find the direction of force where direction of field and current is given, use left hand rule and if direction of current is not given and direction of movement is only given, then use right hand rule.