What is the cause of charging?

A hollow metal sphere of radius 5cm is charged such that potential on its surface is 10 V. What is the potential at the centre of the sphere?

The cause of charging is ......... of electrons from ..... to ............

Two identical cells each of emf \(\epsilon\), having negligible internal resistance r, are connected in parallel with each other across an external resistance R. What is the current through this resistance.

Why is potentiometer preferred over a voltmeter for determining the emf of a cell?

In the northern hemisphere, do magnetic lines of force due to earth's field point towards or away from earth ?

The cross product \(\overrightarrow { E } \times \overrightarrow { B } \)  (where \(\overrightarrow { E } \) = electric field vector \(\overrightarrow { B } \) and  is the magnetic field vector) always gives the ....... of electromagnetic wave.

Sketch the electric field lines for a uniformly charged hollow cylinder as shown in the figure.

Ordinary rubber is an insulator. But the special rubber tyres of aircraft's are made slightly conducting. Why is this necessary?

Consider two hollow concentric spheres, S₁ and S₂ enclosing charges 2Q and 4Q respectively as shown in the figure.
(i) Find out the ratio of the electric flux through them.
(ii) How will the electric flux through the sphere S₁ change, if a medium of dielectric constant \({ \varepsilon }_{ r }\) is introduced in the space inside S₁ in place of air? Deduce the necessary expression.
                       

Two point charges q₁ and q₂ are located at r₁ and r₂ respectively in an external electric field E. Obtain the expression for the total work done in assembling this configuration.

What is the force between two small charged spheres having charges of 2 \(\times\) 10^-7C and 3 \(\times\) 10^-7C placed 30 cm apart in air?

In a parallel plate capacitor with air between the plates, each plate has an area of 6\(\times\)10^-3m² and the distance between the plates is 3 mm. Calculate the capacitance if this capacitor. If this capacitor is connected to a 100 V supply, what is the charge on each plate of the capacitor?

Which of the following figures cannot possibly represent electrostatic field lines?

A 100 resistor is connected to a 220V, 50Hz ac supply.
(a) What is the rms value of current in the circuit?
(b) What is the net power consumed over a full cycle?

(i) Write the basic nuclear process involved in the emission of β⁺ in a symbolic form by a radioactive nucleus.
(ii) In the reactions given below:
(a) \(_{ 6 }^{ 11 }{ C }\rightarrow _{ y }^{ z }{ B }+x+v\)
(b) \(_{ 6 }^{ 12 }{ C }\rightarrow _{ 6 }^{ 12 }{ C }+_{ 6 }^{ 20 }{ Ne }+_{ b }^{ c }{ He }\) 
Find the values of x,y and z and a,b and c.

Carbon silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy bandgap respectively equal to \(({ E }_{ g })_{ C },\ ({ E }_{ g })_{ Si },\) and \(({ E }_{ g })_{ Ge }\). Which of the following statements is true?
(a)\(({ E }_{ g })_{ Si }<({ E }_{ g })_{ Ge }<({ E }_{ g })_{ c }\)
(b)\(({ E }_{ g })_{ c }<({ E }_{ g })_{ Ge }<({ E }_{ g })_{ Si }\)
(c)\(({ E }_{ g })_{ c }>({ E }_{ g })_{ Si }>({ E }_{ g })_{ Ge }\)
(d) \(({ E }_{ g })_{ c }=({ E }_{ g })_{ Si }=({ E }_{ g })_{ Ge }\)

What is the decimal number of binary number \((111001.01)_{ 2 }\)

The graph of potential barrier versus width of depletion region for an unbiased diode is shown in A. In comparison to A, graphs B and C are obtained after biasing the diode in different ways. Identify the type of biasing in B & C and justify your answer.


Explain why:
LEDs are made of compound semiconductor and not by elemental semiconductors. 

The carrier frequency of a station is 40 MHz. A resistor of 10 \(k\Omega \) and a capacity of 12 pF are available in the detector circuit. Is it good enough for detection? Explain.

A modulating signal is a square wave as shown in the figure.
The carrier wave is given by c(T) = 2 sin (8\(\pi \) t) volt.

(i) Sketch the amplitude modulated waveform
(ii) What is the modulation index?

The diagram given below represents the block diagram of a generalised communication system. Identify the elements labelled as X, Y, Z in this diagram. Explain the function of each of these elements.

(a) A point object is placed in front of a double convex lens (of refractive index n =n₂/n₁ with respect air) with its spherical faces of radii of curvature R₁ and R_2.. Show the path of rays due to surface to obtain the formation of the real image of the object.
Hence obtain the lens maker's formula for a thin lens.
(b) A double convex lens having both faces of the same radius of curvature has refractive index 1.55. Find out the radius of curvature of the lens required to get the focal length of 20 cm.