Incorrect statement are :-
(a) A.C. meters can measure D.C also
(b) If A.C. meter measures D.C. there scale must be linear and uniform
(c) A.C. and D.C. meters are based on heating effect of current
(d) A.C. meter reads rms value of current

Options

A. a,b
B. b,c
C. c,d
D. d,a

Answer

To determine which statements about AC and DC meters are incorrect, we need to analyze each statement based on the principles of operation for both types of meters.

### Step-by-Step Solution:

1. **Statement (a): A.C. meters can measure D.C. also.**
- AC meters operate based on the heating effect of current. When DC flows through an AC meter, it will still produce heat, and thus, the meter can measure the current. Therefore, this statement is **correct**.

2. **Statement (b): If A.C. meter measures D.C. their scale must be linear and uniform.**
- The deflection of the needle in an AC meter is related to the square of the current (I²) due to the heating effect. This means that the scale is non-linear and non-uniform because the relationship between current and deflection is quadratic. Therefore, this statement is **incorrect**.

3. **Statement (c): A.C. and D.C. meters are based on the heating effect of current.**
- This statement is incorrect because DC meters operate based on the magnetic effect of current, while AC meters operate based on the heating effect. Therefore, this statement is **incorrect**.

4. **Statement (d): A.C. meter reads rms value of current.**
- AC meters are designed to read the root mean square (RMS) value of the alternating current. This is a correct statement as the heating effect in AC meters is proportional to the square of the RMS current. Therefore, this statement is **correct**.

### Conclusion:
The incorrect statements are:
- (b) If A.C. meter measures D.C. their scale must be linear and uniform.
- (c) A.C. and D.C. meters are based on the heating effect of current.

### Final Answer:
The incorrect statements are (b) and (c).

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