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

(i) Find the value of the phase difference between the current and the voltage in the series LCR circuit shown below. Which one leads in phase : current or voltage ?

(ii) Without making any other change, find the value of the additional capacitor C₁, to be connected in parallel with the capacitor C, in order to make the power factor of the circuit unity.

Define the term 'amplitude modulation'

Explain any two factors which justify the need for modulating a low frequency base-band signal.

Find the wavelength of the electron orbiting in the first excited state in hydrogen atom.

A zener diode is fabricated by heavily doping both p- and n- sides of the junction. Explain, why?

Explain briefly with the help of necessary diagrams, the forward biasing of a p-n junction diode. Also draw characteristic curves.

Explain briefly with the help of necessary diagrams, the  reverse biasing of a p-n junction diode. Also draw characteristic curves.

Draw a schematic sketch showing how amplitude modulated signal is obtained by superposing a modulating signal over a sinusoidal carrier wave.

Write two advantages of frequency modulation over amplitude modulation.

If light of wavelength 412.5 nm is incident on each of the metals given below, which ones will show photoelectric emission and why?

A student wants to use two p-n junction diodes to convert alternating current into direct current. Draw the labelled circuit diagram she would use and explain how it works.

A source of ac voltage v = v₀ sin ωt, is connected across a pure inductor of inductance L. Derive the expressions for the instantaneous current in the circuit. Show that average power dissipated in the circuit is zero.

Define the term "cut off frequency" in photoelectric emission. The threshod frequency of a metal is f. When the light of frequency 2f is incident on the metal plate, the maximum velocity of photo-electrons is v₁. When the frequency of the incident radiation is increased to 5f, the maximum velocity of phto-electrons is v₂. Find the ratio v₁ : v₂.

In a series LCR circuit, obtain the condition under which the impedance of the circuit is minimum ?

In a series LCR circuit, obtain the condition under which watt-less current flows in the circuit ?

Explain, with the help of a circuit diagram, the working of a photo-diode. Write briefly how it is used to detect the optical signals.

Mention the important considerations required while fabricating a p-n junction diode to be used as a Light Emitting Diode (LED). What should be the order of band gap of an LED if it is required to emit light in the visible range?

What are permanent magnets? Give one example ?

Write three important factors which justify the need of modulating a message signal. Show diagrammatically how an amplitude modulated wave is obtained when a modulating signal is superimposed on a carrier wave.

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.