Question

If flow of electric current is parallel to magnetic field, force will be:
(a) Negative
(b) Maximum
(c) Zero
(d) None of these

Answer 1

Hint: We will apply the right hand rule and the formula of force in which the angle between current and field lines becomes parallel resulting in the value of angle as 0. From the right hand rule we will be able to find the directions as well as the force to be normal to current and magnetic fields.

Formula used:
$\overrightarrow{F}=Il\overrightarrow{B}\sin \left( \theta \right)$ where F is force, I is current, B is magnetic field, $\theta $ is the angle between I and B and l is the length of wire.

Complete answer:
Electric current: As the name suggests, the electric current is the flow of electrons inside any material. Whenever this flow takes place then the electrons start moving inside the material resulting into the flow of current inside it. We can see different levels of flow in different materials.

Magnetic field: Magnetic fields are simply fields that are formed around the surface of any charge. These fields will decide the property of the charge related to its becoming of a positive charge or a negative charge.

By the right hand thumb rule, we will find that the current and the magnetic field are separated by some angle while the force is perpendicular to both. We will follow the following diagram for this.

The formula that defines the relation between current and magnetic field is $\overrightarrow{F}=Il\overrightarrow{B}\sin \left( \theta \right)$. Since, I and B are parallel so, the angle $\theta =0$. Thus, $\overrightarrow{F}=Il\overrightarrow{B}\sin \left( 0 \right)$. Since, $\sin \left( 0 \right)=0$ so,

$\begin{align}
  & \overrightarrow{F}=Il\overrightarrow{B}\left( 0 \right) \\
 & \Rightarrow \overrightarrow{F}=0 \\
\end{align}$

So, the correct answer is “Option C”.

Note:
The flow of current inside the metals is greater as compared to others because of the presence of the free electrons present in it. That is why they are also called conductors of electricity. Also, if there is a positive charge then, we will find that the magnetic field lines will be coming in the outward direction of the charge and in case of a negative charge it will come towards the charge. The formula that defines the relation between current and magnetic field is $\overrightarrow{F}=Il\overrightarrow{B}\sin \left( \theta \right)$. Since, I and B are perpendicular so, the angle $\theta =90$. Thus, $\overrightarrow{F}=Il\overrightarrow{B}\sin \left( 90 \right)$. Since, $\sin \left( 90 \right)=1$ so,

$\begin{align}
  & \overrightarrow{F}=Il\overrightarrow{B}\left( 1 \right) \\
 & \Rightarrow \overrightarrow{F}=IlB \\
\end{align}$