Science (English Medium) Class 12 - CBSE Question Bank Solutions

Which of the following combinations should be selected for better tuning of an LCR circuit used for communication?

As the frequency of an ac circuit increases, the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit?

1. Inductor and capacitor.
2. Resistor and inductor.
3. Resistor and capacitor.
4. Resistor, inductor and capacitor.

In series LCR circuit, the plot of I_max vs ω is shown in figure. Find the bandwidth and mark in the figure.

A coil of 0.01 henry inductance and 1 ohm resistance is connected to 200 volt, 50 Hz ac supply. Find the impedance of the circuit and time lag between max. alternating voltage and current.

Consider the LCR circuit shown in figure. Find the net current i and the phase of i. Show that i = v/Z`. Find the impedance Z for this circuit.

For an LCR circuit driven at frequency ω, the equation reads

`L (di)/(dt) + Ri + q/C = v_i = v_m` sin ωt

1. Multiply the equation by i and simplify where possible.
2. Interpret each term physically.
3. Cast the equation in the form of a conservation of energy statement.
4. Integrate the equation over one cycle to find that the phase difference between v and i must be acute.

One requires 11eV of energy to dissociate a carbon monoxide molecule into carbon and oxygen atoms. The minimum frequency of the appropriate electromagnetic radiation to achieve the dissociation lies in ______.

The electric field intensity produced by the radiations coming from 100 W bulb at a 3 m distance is E. The electric field intensity produced by the radiations coming from 50 W bulb at the same distance is ______.

The ratio of contributions made by the electric field and magnetic field components to the intensity of an EM wave is ______.

Why does microwave oven heats up a food item containing water molecules most efficiently?

The magnetic field of a beam emerging from a filter facing a floodlight is given by B₀ = 12 × 10^–8 sin (1.20 × 10⁷z – 3.60 × 10¹⁵t) T. What is the average intensity of the beam?

Electromagnetic waves with wavelength

1. λ₁ is used in satellite communication.
2. λ₂ is used to kill germs in water purifies.
3. λ₃ is used to detect leakage of oil in underground pipelines.
4. λ₄ is used to improve visibility in runways during fog and mist conditions.

1. Identify and name the part of electromagnetic spectrum to which these radiations belong.
2. Arrange these wavelengths in ascending order of their magnitude.
3. Write one more application of each.

What happens to the intensity of light from a bulb if the distance from the bulb is doubled? As a laser beam travels across the length of a room, its intensity essentially remains constant. What geometrical characteristic of LASER beam is responsible for the constant intensity which is missing in the case of light from the bulb?

Do all the electrons that absorb a photon come out as photoelectrons?

Consider a metal exposed to light of wavelength 600 nm. The maximum energy of the electron doubles when light of wavelength 400 nm is used. Find the work function in eV.

Two monochromatic beams A and B of equal intensity I, hit a screen. The number of photons hitting the screen by beam A is twice that by beam B. Then what inference can you make about their frequencies?

Consider a thin target (10^–2 cm square, 10^–3 m thickness) of sodium, which produces a photocurrent of 100 µA when a light of intensity 100W/m² (λ = 660 nm) falls on it. Find the probability that a photoelectron is produced when a photons strikes a sodium atom. [Take density of Na = 0.97 kg/m³].

Consider a 20 W bulb emitting light of wavelength 5000 Å and shining on a metal surface kept at a distance 2 m. Assume that the metal surface has work function of 2 eV and that each atom on the metal surface can be treated as a circular disk of radius 1.5 Å.

1. Estimate no. of photons emitted by the bulb per second. [Assume no other losses]
2. Will there be photoelectric emission?
3. How much time would be required by the atomic disk to receive energy equal to work function (2 eV)?
4. How many photons would atomic disk receive within time duration calculated in (iii) above?
5. Can you explain how photoelectric effect was observed instantaneously?

A 100 m long antenna is mounted on a 500 m tall building. The complex can become a transmission tower for waves with λ.

A speech signal of 3 kHz is used to modulate a carrier signal of frequency 1 MHz, using amplitude modulation. The frequencies of the sidebands will be ______.