1 cal is equal to:
(A) 10 joules
(B) 4.18 joules
(C) 4.18 dynes
(D) none of these

Explanation:
To determine the correct answer, we need to understand the relationship between calories and joules.

The Relationship between Calories and Joules:
- Both calories and joules are units of energy.
- The calorie (cal) is a unit traditionally used in the field of nutrition and represents the amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius.
- The joule (J) is the standard unit of energy in the International System of Units (SI).

Conversion Factor:
- The conversion factor between calories and joules is 1 cal = 4.18 J.
- This means that 1 calorie is equal to 4.18 joules.

Answer:
(B) 4.18 joules

Explanation:
- From the conversion factor, we can see that 1 calorie is equal to 4.18 joules.
- Therefore, the correct answer is (B) 4.18 joules.

Additional Information:
- The option (A) 10 joules is incorrect because 1 calorie is not equal to 10 joules.
- The option (C) 4.18 dynes is also incorrect because dynes are a unit of force, not energy.
- The option (D) none of these is also incorrect because the correct answer is (B) 4.18 joules.

Conclusion:
- 1 cal is equal to 4.18 joules.
- This conversion factor allows us to convert between calories and joules, which are both units of energy.

(a) 10 joules