Class 12 Physics Lab Experiments

To determine angle of minimum deviation for a given prism

May 28 2023

Aim

(i) To determine angle of minimum deviation for a given prism by plotting a graph between angle of incidence & angle of deviation.
(ii) To determine the refractive index of the material (glass) of the prism.

Apparatus

Drawing board, a white sheet of paper, prism, drawing pins, pencil, half metre scale, office pins, graph paper & protector.

Formulae Used:

The refractive index, μ of the material of the prism is given by:

μ = Sin(A+Dm/2)/Sin (A/2) Where Dm is the angle of minimum deviation & A is the angle of prism.

Calculations:

From graph between angle of incidence, ∠ι and angle of deviation, we get the value of Dm (angle of minimum deviation): Dm = 37.8 ⁰

Thus, μ = Sin(A+Dm/2)/Sin (A/2) = Sin(97.8⁰/2)/Sin 30 ⁰

μ1.5077

S.No.	Angle of incidence ∠ι	Angle of deviation ∠δ
1	35 ⁰	43 ⁰
2	40⁰	38.8⁰
3	45⁰	37.8⁰
4	50⁰	38⁰
5	55⁰	40⁰
6	60⁰	42⁰

Result:

From ∠- ι ∠D graph we see that as ∠ι increases, ∠D first decreases, attains a minimum value (Dm) & then again starts increasing for further increase in ∠ƒ .

Angle of minimum deviation = Dm = 37.8 ⁰

Refraction index of material of prism, μ1.5077