Which of the following cannot be accelerated by applying an electric field?

Options

A. Protons
B. Electrons
C. Neutrons
D. Positrons

Answer

To solve the question "Which of the following cannot be accelerated by applying an electric field?", we will analyze the behavior of different particles in an electric field based on their charge.

### Step-by-Step Solution:

1. **Understanding the Concept of Acceleration in an Electric Field:**
- The force acting on a charged particle in an electric field (E) is given by the formula:
\[ F = Q \times E \]
- Where \( F \) is the force, \( Q \) is the charge of the particle, and \( E \) is the electric field strength.
- The acceleration \( a \) of the particle can be calculated using Newton's second law:
\[ a = \frac{F}{m} = \frac{Q \times E}{m} \]
- Here, \( m \) is the mass of the particle.

2. **Analyzing Different Particles:**
- **Proton:**
- Charge (\( Q \)) = +1e (where e is the elementary charge)
- Mass (\( m \)) = \( 1.67 \times 10^{-27} \) kg
- Since \( Q \) is not zero, the proton will accelerate in an electric field.

- **Electron:**
- Charge (\( Q \)) = -1e
- Mass (\( m \)) = \( 9.1 \times 10^{-31} \) kg
- The electron also has a non-zero charge, so it will accelerate in an electric field.

- **Neutron:**
- Charge (\( Q \)) = 0 (neutrons are neutral)
- Mass (\( m \)) ≈ mass of proton
- Since \( Q \) is zero, the force \( F \) will also be zero, leading to zero acceleration. Therefore, the neutron will not accelerate in an electric field.

- **Positron:**
- Charge (\( Q \)) = +1e (positron is the antiparticle of the electron)
- Mass (\( m \)) = \( 9.1 \times 10^{-31} \) kg (similar to electron)
- The positron has a non-zero charge, so it will accelerate in an electric field.

3. **Conclusion:**
- Among the particles analyzed, the neutron is the only particle that cannot be accelerated by applying an electric field because it has no charge.

### Final Answer:
The particle that cannot be accelerated by applying an electric field is the **neutron**.