Which of the following time measuring devices is most precise

Options

A. A wall clock
B. An atomic clock
C. A digital watch
D. A stop watch.

Explanation

To determine which time measuring device is the most precise among the given options, we will analyze each option based on their precision.

### Step-by-Step Solution:

1. **Identify the Devices**: The options provided are:
- A) Wall Clock
- B) Atomic Clock
- C) Digital Watch
- D) Stopwatch

2. **Understand Precision**: Precision in time measurement refers to how closely the measured time can be repeated and how small the error in measurement can be.

3. **Evaluate Each Device**:
- **Wall Clock**: Generally, wall clocks are mechanical or quartz-based and can have an accuracy of about ±1 minute per day. This makes them less precise.
- **Atomic Clock**: Atomic clocks measure time based on the vibrations of atoms (usually cesium or rubidium). They can maintain accuracy to within one second over millions of years, making them extremely precise.
- **Digital Watch**: Digital watches can be more accurate than wall clocks, often within ±15 seconds per month, but they are still not as precise as atomic clocks.
- **Stopwatch**: A stopwatch can measure time intervals with high precision (to the nearest hundredth of a second), but it is still not as accurate over long periods as an atomic clock.

4. **Conclusion**: After evaluating the precision of each device, it is clear that the atomic clock (Option B) is the most precise time measuring device among the options provided.

### Final Answer:
**B) Atomic Clock**