Science (English Medium) कक्षा १२ - CBSE Important Questions for Physics

A capacitor has been charged by a dc source. What are the magnitude of conduction and displacement current, when it is fully charged?

When an ideal capacitor is charged by a dc battery, no current flows. However, when an ac source is used, the current flows continuously. How does one explain this, based on the concept of displacement current?

Answer briefly.

Give two uses of radio waves.

Arrange the following electromagnetic radiation in the ascending order of their frequencies:

X-rays, microwaves, gamma rays, radio waves

Write two uses of the following radiation.

Gamma rays

A giant refracting telescope has an objective lens of focal length 15 m. If an eye piece of focal length 1.0 cm is used, what is the angular magnification of the telescope ?

If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens ? the diameter of the moon is 3.48 × 10⁶ m and the radius of lunar orbit is 3.8 × 10⁸m.

The total magnification produced by a compound microscope is 20. The magnification produced by the eye piece is 5. The microscope is focussed on a certain object. The distance between the objective and eyepiece is observed to be 14 cm. If least distance of distinct vision is 20 cm, calculate the focal length of the objective and the eye piece.

State the condition under which a large magnification can be achieved in an astronomical telescope.

Write the necessary conditions for the phenomenon of total internal reflection to

occur ?

Write the relation between the refractive index and critical angle for a given pair of optical media?

In the meterbridge experimental set up, shown in the figure, the null point ‘D’ is obtained at a distance of 40 cm from end A of the meterbridge wire. If a resistance of 10Ω is connected in series with R₁, null point is obtained at AD = 60 cm. Calculate the values of R₁ and R₂.

Draw a ray diagram showing the image formation by a compound microscope. Hence obtained expression for total magnification when the image is formed at infinity.

Distinguish between myopia and hypermetropia. Show diagrammatically how these defects can be corrected.

What is linearly polarized light? 

Describe briefly using a diagram how sunlight is polarised ?

One day Chetan’s mother developed a severe stomach ache all of a sudden. She was rushed to the doctor who suggested for an immediate endoscopy test and gave an estimate of expenditure for the same. Chetan immediately contacted his class teacher and shared the information with her. The class teacher arranged for the money and rushed to the hospital. On realizing that Chetan belonged to a below average income group family, even the doctor offered concession for the test fee. The test was conducted successfully.

Answer the following questions based on the above information:

(a) Which principle in optics is made use of in endoscopy?

(b) Briefly explain the values reflected in the action taken by the teacher.

(c) In what way do you appreciate the response of the doctor on the given situation?

Define magnifying power of a telescope. Write its expression.

A small telescope has an objective lens of focal length 150 cm and an eye piece of focal length 5 cm. If this telescope is used to view a 100 m high tower 3 km away, find the height of the final image when it is formed 25 cm away from the eye piece.