M.C.Q (1 Marks)

MCQ 11 Mark

prism can produce a minimum deviation $\delta$ in a light beam. If three such prisms are combined, the minimum deviation that can be produced in this beam is:

A
$0$
✓
$\delta$
C
$2\delta$
D
$3\delta$

Answer

Correct option: B.

$\delta$

Explanation:
In combination (refractive angles of prisms reversed with respect to each other), the deviations through two prisms cancel out each other and the net deviation is due to the third prism only.

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MCQ 21 Mark

If a glass prism is dipped in water, its dispersive power:

A
Increases.
✓
Decreases.
C
Does not change.
D
May increase or decrease depending on whether the angle of the prism is less than or greater than 60°.

Answer

Correct option: B.

Decreases.

Explanation:
If $\mu$ is the refractive index and A is the angle of prism, then the angular dispersion produced by the prism will be given by $\delta=(\mu-1)\text{A}.$
Because the relative refractive index of glass with respect to water is small compared to the refractive of glass with respect to air, the dispersive power of the glass prism is more in air than that in water.

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MCQ 31 Mark

In producing a pure spectrum, the incident light is passed through a narrow slit placed in the focal plane of an achromatic lens because a narrow slit:

A
Produces less diffraction.
B
Increases intensity.
C
Allows only one colour at a time.
✓
Allows a more parallel beam when it passes through the lens.

Answer

Correct option: D.

Allows a more parallel beam when it passes through the lens.

Explanation:
To produce a pure spectrum, a parallel light beam is required to be incident on the dispersing element. So, the incident light is passed through a narrow slit placed in the focal plane of an achromatic lens.

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MCQ 41 Mark

The angular dispersion produced by a prism:

✓
Increases if the average refractive index increases.
B
Increases if the average refractive index decreases.
C
Remains constant whether the average refractive index increases or decreases.
D
Has no relation with average refractive index.

Answer

Correct option: A.

Increases if the average refractive index increases.

Explanation:
If $\mu$ is the average refractive index and A is the angle of prism, then the angular dispersion produced by the prism is given by $\delta=(\mu-1)\text{A}.$

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MCQ 51 Mark

Consider the following two statements:

Line spectra contain information about atoms.
Band spectra contain information about molecules.

A
Both $A$ and $B$ are wrong
B
$A$ is correct but $B$ is wrong.
C
$B$ is correct but $A$ is wrong
✓
Both $A$ and $B$ are correct.

Answer

Correct option: D.

Both $A$ and $B$ are correct.

Because line spectra contain wavelengths that are absorbed by atoms and band spectra contain bunch wavelengths that are absorbed by molecules, both statements are correct.

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MCQ 61 Mark

The focal length of a converging lens are $\mathrm{f}_{\mathrm{V}}$ and $\mathrm{f}_{\mathrm{r}}$ for violet and red light respectively:

A
$f_v > f_r$
B
$f_v - f_r$
✓
$f_v < f_r$
D
Any of the three is possible depending on the value of the average refractive index $\mu$.

Answer

Correct option: C.

$f_v < f_r$

Focal length is inversely proportional to refractive index and refractive index is inversely proportional to $\lambda^2.$
So, keeping other parameters the same, we can say:
$\text{f}\propto\frac{1}{\lambda^2}\ \ (\because\lambda_\text{r}<\lambda_\upsilon)$
$\therefore\text{f}_\text{v}<\text{f}_\text{r}$

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Physics M.C.Q (1 Marks)

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