In which of the following photocell is not used ?

Options

A. Burglar alarm
B. Television camera
C. Automatic street lights
D. Vacuum cleaner

Answer

To determine in which of the following devices a photocell is not used, we can analyze each option given:

1. **Burglar Alarm**: A burglar alarm often uses a photocell to detect light changes. For instance, if a light beam is interrupted, it can trigger the alarm. Thus, a photocell is used in burglar alarms.

2. **Television Camera**: A television camera captures images using light. It relies on light energy to function, which means it also utilizes a photocell to convert light into electrical signals. Therefore, a photocell is used in television cameras.

3. **Automatic Streetlights**: Automatic streetlights use photocells to detect the ambient light levels. When it gets dark, the photocell activates the streetlight. Hence, photocells are essential in automatic streetlights.

4. **Vacuum Cleaner**: A vacuum cleaner operates using electrical energy (usually from a power outlet) to create suction and does not rely on light energy for its operation. It does not use a photocell.

Based on this analysis, the device in which a photocell is not used is the **vacuum cleaner**.

### Final Answer:
The photocell is not used in a **vacuum cleaner**.