Whenever a stream of clectrons collides with a stream of photons, in this collision, which of the following is not conserved?

Options

A. a. Linear momentum
B. b. Total energy
C. c. No. of photons
D. d. No. of electrons

Explanation

To solve the question regarding the conservation laws during the collision of a stream of electrons with a stream of photons, we can follow these steps:

### Step 1: Understand the Nature of the Particles
- **Electrons** are charged particles with mass, while **photons** are massless particles that carry energy and momentum but do not have charge.
- When these two streams collide, they can interact in ways that involve energy transfer.

### Step 2: Identify Conservation Laws
- In physics, during collisions or interactions, certain quantities are conserved. The key conservation laws to consider here are:
- **Conservation of Linear Momentum**
- **Conservation of Total Energy**
- **Conservation of Number of Particles**

### Step 3: Analyze Each Conservation Law
- **Linear Momentum**:
- In the collision, both electrons and photons have momentum. The total momentum before the collision must equal the total momentum after the collision. Thus, linear momentum is conserved.

- **Total Energy**:
- The total energy before the collision (kinetic energy of electrons and energy of photons) must equal the total energy after the collision. Since photons can transfer energy to electrons, total energy is conserved.

- **Number of Photons**:
- When a photon collides with an electron, it can be absorbed by the electron, effectively reducing the number of photons in the system. Therefore, the number of photons is not conserved.

- **Number of Electrons**:
- The number of electrons remains constant as they do not disappear or get created in this interaction.

### Step 4: Conclusion
- Based on the analysis, the quantity that is **not conserved** during the collision of a stream of electrons with a stream of photons is the **number of photons**.

### Final Answer
The correct option is: **C. Number of photons**

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