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

A point charge Q is placed at the origin. Find the electrostatic energy stored outside the sphere of radius R centred at the origin.

A metal sphere of radius R is charged to a potential V.

1. Find the electrostatic energy stored in the electric field within a concentric sphere of radius 2 R.
2. Show that the electrostatic field energy stored outside the sphere of radius 2 R equals that stored within it.

A large conducting plane has a surface charge density `1.0 xx 10^-4  "Cm"^-2` . Find the electrostatic energy stored in a cubical volume of edge 1⋅0 cm in front of the plane.

Figure shows two identical parallel plate capacitors connected to a battery through a switch S. Initially, the switch is closed so that the capacitors are completely charged. The switch is now opened and the free space between the plates of the capacitors is filled with a dielectric of dielectric constant 3. Find the ratio of the initial total energy stored in the capacitors to the final total energy stored.

Obtain the expression for the energy stored in a capacitor connected across a dc battery. Hence define energy density of the capacitor

Define internal resistance of a cell.

The cold junction of a thermocouple is maintained at 10ºC. No thermo e.m.f. is developed when the hot junction is maintained at 530ºC. The neutral temperature is ______.

Do free electrons travel to region of higher potential or lower potential?

Prove that, if an insulated, uncharged conductor is placed near a charged conductor and no other conductors are present, the uncharged body must be intermediate in potential between that of the charged body and that of infinity.

Consider the circuit arrangement shown in figure (a) for studying input and output characteristics of npn transistor in CE configuration.

(a)

(b)

Select the values of R_B and R_C for a transistor whose V_BE = 0.7 V, so that the transistor is operating at point Q as shown in the characteristics shown in figure (b). Given that the input impedance of the transistor is very small and V_CC = V_BB = 16 V, also find the voltage gain and power gain of the circuit making appropriate assumptions.

A parallel plate capacitor (A) of capacitance C is charged by a battery to voltage V. The battery is disconnected and an uncharged capacitor (B) of capacitance 2C is connected across A. Find the ratio of total electrostatic energy stored in A and B finally and that stored in A initially.

An ammeter of resistance 0.81 ohm reads up to 1 A. The value of the required shunt to increase the range to 10 A is ______.

Sketch the change in flux, emf and force when a conducting rod PQ of resistance R and length l moves freely to and fro between A and C with speed v on a rectangular conductor placed in uniform magnetic field as shown in the figure

Describe, with the help of a circuit diagram, the working of Zener diode as a voltage regulator.

Two large conducting spheres carrying charges Q₁ and Q₂ are brought close to each other. Is the magnitude of the electrostatic force between them exactly given by Q₁ Q₂/4π∈₀r ², where r is the distance between their centres?

In a Van de Graaff type generator a spherical metal shell is to be a 15 × 10⁶ V electrode. The dielectric strength of the gas surrounding the electrode is 5 × 10⁷ Vm⁻¹. What is the minimum radius of the spherical shell required? (You will learn from this exercise why one cannot build an electrostatic generator using a very small shell which requires a small charge to acquire a high potential.)

A small sphere of radius r₁ and charge q₁ is enclosed by a spherical shell of radius r₂ and charge q₂. Show that if q₁ is positive, charge will necessarily flow from the sphere to the shell (when the two are connected by a wire) no matter what the charge q₂ on the shell is.

In the following diagram, an object 'O' is placed 15 cm in front of a convex lens L₁ of focal length 20 cm and the final image is formed at I at a distance of 80 cm from the second lens L₂. Find the focal length of the lens L₂.

Explain, with the help of a circuit diagram, the principle and working of a Zener diode as voltage regular.

Draw the circuit diagram of zener diode as a voltage regulator and briefly explains its working ?