Science (English Medium) Class 12 - CBSE Question Bank Solutions

A battery of emf 100 V and a resistor of resistance 10 kΩ are joined in series. This system is used as a source to supply current to an external resistance R. If R is not greater than 100 Ω, the current through it is constant up to two significant digits.
Find its value. This is the basic principle of a constant-current source.

Find the equivalent resistance of the network shown in the figure between the points a and b.

How many time constants will elapse before the power delivered by a battery drops to half of its maximum value in an RC circuit?

Apply the first law of thermodynamics to a resistor carrying a current i. Identify which of the quantities ∆Q, ∆U and ∆W are zero, positive and negative.

Do all thermocouples have a neutral temperature?

Do the electrodes in an electrolytic cell have fixed polarity like a battery?

A coil of resistance 100 Ω is connected across a battery of emf 6.0 V. Assume that the heat developed in the coil is used to raise its temperature. If the heat capacity of the coil is 4.0 J K⁻¹, how long will it take to raise the temperature of the coil by 15°C?

The temperatures of the junctions of a bismuth-silver thermocouple are maintained at 0°C and 0.001°C. Find the thermo-emf (Seebeck emf) developed. For bismuth-silver, a = − 46 × 10⁻⁶ V°C⁻¹ and b = −0.48 × 10⁻⁶ V°C⁻².

A plate of area 10 cm² is to be electroplated with copper (density 9000 kg m⁻³) to a thickness of 10 micrometres on both sides, using a cell of 12 V. Calculate the energy spent by the cell in the process of deposition. If this energy is used to heat 100 g of water, calculate the rise in the temperature of the water. ECE of copper = 3 × 10⁻⁷ kg C⁻¹and specific heat capacity of water = 4200 J kg⁻¹.

When a boron nucleus `(""_5^10"B")` is bombarded by a neutron, a α-particle is emitted. Which nucleus will be formed as a result?

The graph of ln `("R"/"R"_0)` versus ln A (R = radius of a nucleus and A = its mass number) is ______.

Two lithium nuclei in a lithium vapour at room temperature do not combine to form a carbon nucleus because

Derive the relation a sin θ = λ  for the first minimum of the diffraction pattern produced due to a single slit of width ‘a’ using light of wavelength λ.

Using the monochromatic light of same wavelength in the experimental set-up of the diffraction pattern  as well as in the interference pattern where the slit separation is 1 mm, 10 interference fringes are found  to be within the central maximum of the diffraction pattern. Determine the width of the single slit, if the  screen is kept at the same distance from the slit in the two cases.

Electric charges are distributed in a small volume. The flux of the electric field through a spherical surface of radius 10 cm surrounding the total charge is 25 V m. The flux over a concentric sphere of radius 20 cm will be _____________ .

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.

Derive the relation a sin θ = λ for the first minimum of the diffraction pattern produced due to a single slit of width 'a' using light of wavelength λ.

The electric flux through a closed Gaussian surface depends upon ______.

Answer the following question.

A cell of emf E and internal resistance r is connected across a variable resistor R. Plot the shape of graphs showing a variation of terminal voltage V with (i) R and (ii) circuit current I.

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.