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

The figure shows experimental set up of a meter bridge. When the two unknown resistances X and Y are inserted, the null point D is obtained 40 cm from the end A. When a resistance of 10 Ω is connected in series with X, the null point shifts by 10 cm. Find the position of the null point when the 10 Ω resistance is instead connected in series with resistance ‘Y’. Determine the values of the resistances X and Y.

Obtain the expression for the current flowing through a conductor having number density of the electron n, area of cross-section A in terms of the drift velocity v_d . 

How does the resistivity of a semiconductor change with rise of temperature ? Explain.

Answer the following question.
How is the drift velocity in a conductor affected with the rise in temperature?

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.

A student uses the circuit diagram of a potentiometer as shown in the figure
(a) for a steady current I passing through the potentiometer wire, he gets a null point for the cell ε₁. and not for ε₂. Give the reason for this observation and suggest how this difficulty can be resolved.

(b) What is the function of resistance R used in the circuit? How will the change in its value affect the null point?

(c) How can the sensitivity of the potentiometer be increased?

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.