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

Mention two main sources of power loss in real transformers.

Which of the following cannot modify an external magnetic field as shown in the figure?

The relative magnetic permeability of a substance X is slightly less than unity and that of substance Y is slightly more than unity, then ______.

The large scale transmission of electrical energy over long distances is done with the use of transformers. The voltage output of the generator is stepped-up because of ______.

How does the electric flux due to a point charge enclosed by a spherical Gaussian surface get affected when its radius is increased?

Two cells of emfs 1.5 V and 2.0 V,  having internal resistances 0.2 Ω and 0.3 Ω, respectively, are connected in parallel. Calculate the emf and internal resistance of the equivalent cell.

The plot of the variation of potential difference across a combination of three identical cells in series, versus current is shown below. What is the emf and internal resistance of each cell ?

A battery of emf 12 V and internal resistance 2 Ω is connected to a 4 Ω resistor as shown in the figure.

(a) Show that a voltmeter when placed across the cell and across the resistor, in turn, gives the same reading.

(b) To record the voltage and the current in the circuit, why is voltmeter placed in parallel and ammeter in series in the circuit?

Two identical cells of emf 1.5 V each joined in parallel, supply energy to an external circuit consisting of two resistances of 7 Ω each joined in parallel. A very high resistance voltmeter reads the terminal voltage of cells to be 1.4 V. Calculate the internal resistance of each cell.

Deduce the expression for the potential energy of a system of two charges q₁ and q₂ located `vec(r_1)` and `vec(r_2)`, respectively, in an external electric field.

Define electric flux.

Write S.I unit of electric flux.

Find out the outward flux to a point charge +q placed at the centre of a cube of side ‘a’. Why is it found to be independent of the size and shape of the surface enclosing it? Explain.

Distinguish between emf and terminal voltage of a cell.

"The outward electric flux due to charge +Q is independent of the shape and size of the surface which encloses is." Give two reasons to justify this statement.

What is the electric flux through a cube of side 1 cm which encloses an electric dipole?

A proton and an α-particle have the same de-Broglie wavelength Determine the ratio of  their speeds.

A cell of emf 'E' and internal resistance 'r' is connected across a variable load resistor R. Draw the plots of the terminal voltage V versus (i) R and (ii) the current I.

It is found that when R = 4 Ω, the current is 1 A and when R is increased to 9 Ω, the current reduces to 0.5 A. Find the values of the emf E and internal resistance r.

Given the electric field in the region `vecE=2xhati`, find the net electric flux through the cube and the charge enclosed by it.

Given a uniform electric field `vecE=5xx10^3hati`N/C, find the flux of this field through a square of 10 cm on a side whose plane is parallel to the y-z plane. What would be the flux through the same square if the plane makes a 30° angle with the x-axis ?