Science (English Medium) Class 12 - CBSE Important Questions

Derive the equation of the balanced state in a Wheatstone bridge using Kirchhoff’s laws.

A conductor of 10 Ω is connected across a 6 V ideal source. The power supplied by the source to the conductor is ______.

Two cells of emf E₁ and E₂ and internal resistances r₁ and r₂ are connected in parallel, with their terminals of the same polarity connected together. Obtain an expression for the equivalent emf of the combination.

The potential difference applied across a given conductor is doubled. How will this affect (i) the mobility of electrons and (ii) the current density in the conductor? Justify your answers.

A potential difference (V) is applied across a conductor of length 'L' and cross-sectional area 'A'.

How will the drift velocity of electrons and the current density be affected if another identical conductor of the same material were connected in series with the first conductor? Justify your answers.

• Assertion (A): The given figure does not show a balanced Wheatstone bridge.
• Reason (R): For a balanced bridge small current should flow through the galvanometer.

Two conductors, made of the same material have equal lengths but different cross-sectional areas A₁ and A₂ (A₁ > A₂). They are connected in parallel across a cell. Show that the drift velocities of electrons in two conductors are equal.

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 ______.

Write Maxwell's generalization of Ampere's circuital law. Show that in the process of charging a capacitor, the current produced within the plates of the capacitor is `I=varepsilon_0 (dphi_E)/dt,`where Φ_E is the electric flux produced during charging of the capacitor plates.

Write Maxwell's generalization of Ampere's circuital law. Show that in the process of charging a capacitor, the current produced within the plates of the capacitor is `I=varepsilon_0 (dphi_E)/dt,`where Φ_E is the electric flux produced during charging of the capacitor plates.

Use Biot-Savart law to derive the expression for the magnetic field on the axis of a current carrying circular loop of radius R.

Draw the magnetic field lines due to a circular wire carrying current I.

Why does a galvanometer show a momentary deflection at the time of charging or discharging a capacitor? Write the necessary expression to explain this observation.

What can be the causes of helical motion of a charged particle?

State the principle of a cyclotron.

Show that the time period of revolution of particles in a cyclotron is independent of their speeds. Why is this property necessary for the operation of a cyclotron?

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

Electron drift speed is estimated to be of the order of mm s⁻¹. Yet large current of the order of few amperes can be set up in the wire. Explain briefly.

Derive the expression for the magnetic field due to a solenoid of length ‘2l’, radius ‘a’ having ’n’ number of turns per unit length and carrying a steady current ‘I’ at a point
on the axial line, distance ‘r’ from the centre of the solenoid. How does this expression compare with the axial magnetic field due to a bar magnet of magnetic moment ‘m’?

Define the term self-inductance of a solenoid.

How does one understand this motional emf by invoking the Lorentz force acting on the free charge carriers of the conductor? Explain.