Which of the following statements is incorrect?

Options

A. To increase the magnetic strength, increase the number of strokes while creating magnets.
B. To increase the magnetic strength, increase the number of coils around the nail.
C. Magnetic force is a pulling force only.
D. Magnet may lose its magnetic property when heated to a very high temperature.

Explanation

To determine which of the statements is incorrect, we need to analyze the statements provided regarding increasing magnetic strength:

1. **To increase the magnetic strength, increase the number of strokes while creating magnets.**
2. **To increase the magnetic strength, increase the number of coils around the nail.** (This statement is repeated multiple times.)

Now, let's evaluate each statement:

### Step 1: Analyze the first statement
- The first statement suggests that increasing the number of strokes while creating magnets will increase magnetic strength.
- In practice, the strength of a magnet can be influenced by the number of strokes, but it is not the most effective method compared to other factors.

### Step 2: Analyze the second statement
- The second statement emphasizes increasing the number of coils around a nail (which is a common method in electromagnetism).
- It is well-established that increasing the number of coils around a nail (or any core material) does indeed increase the magnetic strength of the electromagnet. This is because more coils create a stronger magnetic field.

### Conclusion
- The first statement is less effective and can be considered incorrect in the context of significantly increasing magnetic strength compared to the second statement, which is correct.

### Final Answer
The incorrect statement is: **"To increase the magnetic strength, increase the number of strokes while creating magnets."**

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