Science (English Medium) कक्षा १२ - CBSE Important Questions

A metal sphere is kept on an insulting stands. A negatively charged rod is brought near it, then the sphere is  earthed as shown. On removing the earthing, and taking the negatively charged rod away, what will be the  nature of charge on the sphere? Give reason for your answer. 

Solve the following question.
Using Kirchhoff’s rules, calculate the current through the 40 Ω and 20 Ω  resistors in the following circuit. 

Answer the following question.
What is the end error in a meter bridge? How is it overcome? The resistances in the two arms of the metre bridge are R = Ω and S respectively.  When the resistance S is shunted with equal resistance, the new balance length found to be 1.5 l₁, where l₂ is the initial balancing length. calculate the value of s.

A conductor of length ‘l’ is rotated about one of its ends at a constant angular speed ‘ω’ in a plane perpendicular to a uniform magnetic field B. Plot graphs to show variations of the emf induced across the ends of the conductor with

1. angular speed ω and
2. length of the conductor l.

Define Current density.

A current of 0.8 A flows in a conductor of 40 Ω for 1 minute. The heat produced in the conductor will be ______.

A cell of emf E is connected across an external resistance R. When current 'I' is drawn from the cell, the potential difference across the electrodes of the cell drops to V. The internal resistance 'r' of the cell is ______.

Define relaxation time.

Derive an expression for resistivity of a conductor in terms of the number density of charge carriers in the conductor and relaxation time.

Obtain an expression for the energy stored in a solenoid of self-inductance ‘L’ when the current through it grows from zero to ‘I’.

Find the condition under which the charged particles moving with different speeds in the presence of electric and magnetic field vectors can be used to select charged particles of a particular speed.

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

Sketch a schematic diagram depicting oscillating electric and magnetic fields of an em wave propagating along + z-direction ?

Two long straight parallel conductors 'a' and 'b', carrying steady currents I_a and I_b are separated by a distance d. Write the magnitude and direction of the magnetic field produced by the conductor 'a' at the points along the conductor 'b'. If the currents are flowing in the same direction, what is the nature and magnitude of the force between the two conductors?

Show with the help of a diagram how the force between the two conductors would change when the currents in them flow in the opposite directions?

 Two infinitely large plane thin parallel sheets having surface charge densities σ₁ and σ₂ (σ₁ > σ₂) are shown in the figure. Write the magnitudes and directions of the net fields in the regions marked II and III.

The motion of copper plate is damped when it is allowed to oscillate between the two poles of a magnet. What is the cause of this damping?

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.

Define mutual inductance between two long coaxial solenoids. Find out the expression for the mutual inductance of inner solenoid of length l having the radius r₁ and the number of turns n₁ per unit length due to the second outer solenoid of same length and r₂ number of turns per unit length.

A rectangular loop of size l × b carrying a steady current I is placed in a uniform magnetic field `vecB`. Prove that the torque  `vectau`acting on the loop is give by `vectau =vecm xx vecB,`where `vecm` is the magnetic moment of the loop.