Science (English Medium) कक्षा १२ - CBSE Important Questions

Output characteristics of an n-p-n transistor in CE configuration is shown in the figure.

Determine:

(i) dynamic output resistance

(ii) dc current gain and

(iii) ac current gain at an operating point V_CE = 10 V, when I_B = 30 μA.

The figure shows a series LCR circuit with L = 10.0 H, C = 40 μF, R = 60 Ω connected to a variable frequency 240 V source, calculate

(i) the angular frequency of the source which drives the circuit at resonance,

(ii) the current at the resonating frequency,

(iii) the rms potential drop across the inductor at resonance.

An alternative voltage given by V = 140 sin 314t is connected across a pure resistor of 50 Ω. Find

1. The frequency of the source.
2. The rms current is through the resistor.

Name the parts of the electromagnetic spectrum which is

used to treat muscular strain.

Write in brief, how these waves can be produced.

Name the parts of the electromagnetic spectrum which is

used as a diagnostic tool in medicine.

Write in brief, how these waves can be produced.

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

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?

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.

How is the working of a telescope different from that of a microscope?

The focal lengths of the objective and eyepiece of a microscope are 1.25 cm and 5 cm respectively. Find the position of the object relative to the objective in order to obtain an angular magnification of 30 in normal adjustment.

A ray of light passes through a prism of refractive index `sqrt2` as shown in the figure. Find:

1. The angle of incidence (∠r₂) at face AC.
2. The angle of minimum deviation for this prism.