A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region. If an electron is projected along the direction of the fields with a certain velocity then

Options

A. speed will decrease
B. speed will increase
C. will turn towards left of direction of motion
D. will turn towards right of direction a motion

Answer

To solve the problem step by step, we can follow this approach:

### Step 1: Understand the scenario
We have a uniform electric field (E) and a uniform magnetic field (B) acting in the same direction. An electron is projected along the direction of these fields with a certain velocity (V).

**Hint:** Visualize the setup by drawing the electric field, magnetic field, and the direction of the electron's velocity.

### Step 2: Analyze the forces acting on the electron
When an electron is placed in an electric field, it experiences an electric force given by:
\[ F_E = qE \]
where \( q \) is the charge of the electron (which is negative).

In a magnetic field, the force on a charged particle is given by:
\[ F_B = q(\mathbf{V} \times \mathbf{B}) \]
Since the electron is moving in the same direction as the magnetic field, the cross product \( \mathbf{V} \times \mathbf{B} \) will be zero:
\[ F_B = 0 \]

**Hint:** Remember that the magnetic force depends on the angle between the velocity and the magnetic field. If they are parallel, the magnetic force is zero.

### Step 3: Determine the net force acting on the electron
Since the magnetic force is zero, the only force acting on the electron is the electric force. The direction of the electric force is opposite to the direction of the electric field (since the electron has a negative charge).

**Hint:** Identify the direction of the electric force relative to the velocity of the electron.

### Step 4: Analyze the effect of the electric force
The electric force will cause the electron to decelerate because it acts in the opposite direction to the velocity of the electron. This means that the speed of the electron will decrease over time.

**Hint:** Consider how forces affect motion according to Newton's second law.

### Step 5: Conclusion
Since the electron is experiencing a force that opposes its motion, its speed will decrease. Therefore, the correct conclusion is that the speed of the electron reduces.

**Final Answer:** The speed of the electron decreases.