Science (English Medium) Class 12 - CBSE Important Questions for Physics

A carbon resistor is shown in the figure. Using color code, write the value of the resistance.

Twelve wires each having a resistance of 3 Ω are connected to form a cubical network. A battery of 10 V and negligible internal resistance is connected across the diagonally opposite corners of this network. Determine its equivalent resistance and the current along each edge of the cube.

V-I graph for a metallic wire at two different temperatures T1 and T2 is as shown in the figure. Which of the two temperatures is higher and why?

A variable resistor R is connected across a cell of emf ε and internal resistance r as shown in the figure. Draw a plot showing the variation of
(i) Terminal voltage V and
(ii) the current I, as a function of R.

Sunita and her friends visited the exhibition. The policeman asked them to pass through a metal detector. Sunita's friends were initially scared of it. Sunita, however, explained to them the purpose and working of the metal detector.

Answer the following questions :
(a) On what principle does a metal detector work?
(b) Why does the detector emit a sound when a person carrying any metallic object walks through it?
(c) State any two qualities which Sunita displayed while explaining the purpose of walking through the detector.

Define internal resistance of a cell.

The temperature (T) dependence of resistivity of materials A and material B is represented by fig (i) and fig (ii) respectively. Identify material A and material B.

fig. (i)

fig. (ii)

Two cells of emfs E₁ and E₂ and internal resistances r₁ and r₂ respectively are connected in parallel as shown in the figure. Deduce the expression for the

1. equivalent emf of the combination
2. equivalent internal resistance of the combination
3. potential difference between the points A and B.

State the two Kirchhoff’s rules used in the analysis of electric circuits and explain them.

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.