Science (English Medium) कक्षा १२ - CBSE Question Bank Solutions

In Young's double-slit experiment, the two slits are separated by a distance of 1.5 mm, and the screen is placed 1 m away from the plane of the slits. A beam of light consisting of two wavelengths of 650 nm and 520 nm is used to obtain interference fringes.
Find the least distance from the central maximum where the bright fringes due to both the wavelengths coincide.

Two parallel uniformly charged infinite plane sheets, '1' and '2', have charge densities + `sigma and -2sigma `respectively. Give the magnitude and direction of the net electric field at a point.
(i) in between the two sheets and
(ii) outside near the sheet '1'.

The wavelength and intensity of light emitted by a LED depend upon ______.

What is a solar cell?

Explain the three processes involved in the working of a solar cell.

A uniform magnetic field of 1.5 T exists in a cylindrical region of radius 10.0 cm, its direction parallel to the axis along east to west. A wire carrying current of 7.0 A in the north to south direction passes through this region. What is the magnitude and direction of the force on the wire if,

(a) the wire intersects the axis,

(b) the wire is turned from N-S to northeast-northwest direction,

(c) the wire in the N-S direction is lowered from the axis by a distance of 6.0 cm?

A parallel plate air capacitor is charged to a potential difference of V volts. After disconnecting the charging battery the distance between the plates of the capacitor is increased using an insulating handle. As a result the potential difference between the plates ______.

Current flows through uniform, square frames as shown in the figure. In which case is the magnetic field at the centre of the frame not zero?

Capacitor plates are charged by a battery with ‘V’ volts. After charging the battery is disconnected and a dielectric slab with dielectric constant ‘K’ is inserted between its plates, the potential across the plates of a capacitor will become ____________.

A free electron and a free proton are placed between two oppositely charged parallel plates. Both are closer to the positive plate than the negative plate.

Which of the following statements is true?

1. The force on the proton is greater than the force on the electron.
2. The potential energy of the proton is greater than that of the electron.
3. The potential energy of the proton and the electron is the same.

Name the device which converts the change in intensity of illumination to change in electric current flowing through it. Plot I-V characteristics of this device for different intensities. State any two applications of this device.

In Figure, assuming the diodes to be ideal ______.

The amplifiers X, Y and Z are connected in series. If the voltage gains of X, Y and Z are 10, 20 and 30, respectively and the input signal is 1 mV peak value, then what is the output signal voltage (peak value)

1. if dc supply voltage is 10V?
2. if dc supply voltage is 5V?

If the resistance R₁ is increased (Figure), how will the readings of the ammeter and voltmeter change?

Read the following paragraph and answer the questions.

1. Why are LEDs made of compound semiconductor and not of elemental semiconductors?
2. What should be the order of bandgap of an LED, if it is required to emit light in the visible range?
3. A student connects the blue coloured LED as shown in the figure. The LED did not glow when switch S is closed. Explain why?
   
   OR
   iii. Draw V-I characteristic of a p-n junction diode in
   (i) forward bias and (ii) reverse bias

Why a photo-diode is operated in reverse bias whereas the current in the forward bias is much larger than that in the reverse bias? Explain. Mention its two uses.