The essential difference between an AC generator and a DC generator is that:
(a) AC generator has an electromagnet while a DC generator has permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.

Options

A. AC generator has an electromagnet while a DC generator has permanent magnet
B. DC generator will generate a higher voltage.
C. AC generator will generate a higher voltage.
D. AC generator has slip rings while the DC generator has a commutator

Answer

To solve the question regarding the essential difference between an AC generator and a DC generator, we will analyze each option provided:

1. **Understanding AC and DC Generators**:
- An AC (Alternating Current) generator produces current that periodically reverses direction.
- A DC (Direct Current) generator produces current that flows in a single direction.

2. **Analyzing the Options**:
- **(a)** AC generator has an electromagnet while a DC generator has a permanent magnet.
- This statement is incorrect. Both AC and DC generators can use either electromagnets or permanent magnets. The type of magnet does not define the generator's classification.

- **(b)** DC generator will generate a higher voltage.
- This statement is also misleading. The voltage output depends on the design and application of the generator rather than its classification as AC or DC.

- **(c)** AC generator will generate a higher voltage.
- Similar to option (b), this statement is not universally true. The voltage output is dependent on various factors, including the generator's design.

- **(d)** AC generator has slip rings while the DC generator has a commutator.
- This statement is correct. The essential difference lies in the type of electrical connections used. AC generators use slip rings to allow the current to alternate, while DC generators use a commutator to ensure the current flows in one direction.

3. **Conclusion**:
- After analyzing all options, the correct answer is **(d)** AC generator has slip rings while the DC generator has a commutator. This is the essential difference between the two types of generators.

### Step-by-Step Solution:
1. **Identify the types of generators**: Understand the basic functions of AC and DC generators.
2. **Evaluate each option**: Analyze the statements given in the options to determine their validity.
3. **Determine the correct answer**: Based on the analysis, identify the option that correctly describes the essential difference between AC and DC generators.