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

In viewing through a magnifying glass, one usually positions one’s eyes very close to the lens. Does angular magnification change if the eye is moved back?

A Cassegrain telescope uses two mirrors as shown in the figure. Such a telescope is built with the mirrors 20 mm apart. If the radius of curvature of the large mirror is 220 mm and the small mirror is 140 mm, where will the final image of an object at infinity be?

Two identical parallel plate capacitors A and B are connected to a battery of V volts with the switch S closed. The switch is now opened and the free space between the plates of the capacitors is filled with a dielectric of dielectric constant K. Find the ratio of the total electrostatic energy stored in both capacitors before and after the introduction of the dielectric.

(i) Find equivalent capacitance between A and B in the combination given below. Each capacitor is of 2 µF capacitance.

(ii) If a dc source of 7 V is connected across AB, how much charge is drawn from the source and what is the energy stored in the network? 

Why is it necessary to introduce a radial magnetic field inside the coil of a galvanometer?

Can a galvanometer as such be used for measuring the current? Explain.

Two identical capacitors of 12 pF each are connected in series across a battery of 50 V. How much electrostatic energy is stored in the combination? If these were connected in parallel across the same battery, how much energy will be stored in the combination now?

Also find the charge drawn from the battery in each case.

With the help of a neat and labelled diagram, explain the principle and working of a moving coil galvanometer ?

Define current sensitivity of a galvanometer.

Why does a galvanometer when connected in series with a capacitor show a momentary deflection, when it is being charged or discharged?

How does this observation lead to modifying the Ampere's circuital law?

Hence write the generalised expression of Ampere's law.

A capacitor of unknown capacitance is connected across a battery of V volts. The charge stored in it is 360 μC. When potential across the capacitor is reduced by 120 V, the charge stored in it becomes 120 μC.

Calculate:

(i) The potential V and the unknown capacitance C.

(ii) What will be the charge stored in the capacitor, if the voltage applied had increased by 120 V?

A capacitor of unknown capacitance is connected across a battery of V volts. The charge stored in it is 300 μC. When potential across the capacitor is reduced by 100 V, the charge stored in it becomes 100 μC. Calculate The potential V and the unknown capacitance. What will be the charge stored in the capacitor if the voltage applied had increased by 100 V?

Define the current sensitivity of a galvanometer ?

Write current sensitivity of a galvanomete S.I. unit. 

Figure shows two circuits each having a galvanometer and a battery of 3V.

When the galvanometers in each arrangement do not show any deflection, obtain the ratio R₁/R₂.

A capacitor of capacitance ‘C’ is being charged by connecting it across a dc source along with an ammeter. Will the ammeter show a momentary deflection during the process of charging? If so, how would you explain this momentary deflection and the resulting continuity of current in the circuit? Write the expression for the current inside the capacitor.

Explain, giving reasons, the basic difference in converting a galvanometer into (i) a voltmeter and (ii) an ammeter?

Draw a labelled diagram of a moving coil galvanometer and explain its working. What is the function of radial magnetic field inside the coil?

Draw the circuit for studying the input and output characteristics of and transistor in CE configuration. Show, how, from the output characteristics, the information about the current amplification factor (β_ac) can obtained.

Draw a plot of the transfer characteristics (V₀ versus V_i) for a base-biased transistor in CE configuration. Show for which regions in the plot, the transistor can operate as a switch ?