List of practice Questions

An electromagnetic wave is propagating along x-axis. At any instant, the phase difference between the electric field ($\vec{E}$) and magnetic field ($\vec{B}$) is

In Bohr model, electron transitions from $n=5$ to $n=1$ emit wavelength $\lambda$. What is wavelength for transition $n=5$ to $n=2$?

Assertion (A): On increasing the intensity of incident light of frequency \( v(> v_0) \) on a photosensitive surface, the photocurrent increases. Reason (R): The stopping potential for a photosensitive surface increases with increase of frequency \( v(> v_0) \) of incident light.

Assertion (A): On forward biasing a p-n junction diode, the height of the barrier potential increases. Reason (R): In forward biasing of a p-n junction diode, the direction of the applied voltage is in the same direction as the built-in potential.

Assertion (A): Light added to light can produce darkness. Reason (R): When two coherent light waves interfere, there is darkness at position of destructive interference.

Assertion (A): Two electric heaters of power \( P_1 \) and \( P_2 (> P_1) \) are joined in series across a dc source of voltage \( V \). The power consumed by the combination will be less than that consumed by \( P_1 \) when connected across the same source. Reason (R): The power consumed by an electric device when connected to a dc source of voltage \( V \) is proportional to its resistance.

Write two points of difference between intrinsic and extrinsic semiconductors.

Which of the following materials has positive and small value of magnetic susceptibility?

A galvanometer of resistance $27\ \Omega$ is converted into an ammeter of range $(0 - 10\text{ mA})$ using a resistance of $3\ \Omega$. The galvanometer will show full scale deflection for a current of about

The magnetic flux $\phi = 5At^{2} + Bt - 2C$ has SI units of $A$ and $B$ respectively}

The figure shows the variation of capacitive reactance $X_C$ with $1/\omega$ gives two straight lines for capacitors $C_1$ and $C_2$. The ratio $C_1/C_2$ is

A magnet with north pole down is dropped along the axis of a closed solenoid. Observed from top, the induced current is

Magnetic field due to long wire along y-axis carrying current in -y direction at (50 cm,0,0) points along

The maximum kinetic energy of photoelectrons depends on

In Bohr model, for large $n$, spacing between consecutive orbits is proportional to

A concave mirror produces a two times magnified virtual image of an object kept 10 cm in front of it. Calculate the focal length of the mirror.

State Faraday’s law of electromagnetic induction.

Derive an expression for the self-inductance of an air-filled long solenoid of length \(l\) and cross-sectional area \(A\) having \(N\) turns.

A conducting rod of length 50 cm, with one end pivoted, is rotated with angular speed of 60 rpm in a uniform magnetic field of 4.0 mT directed perpendicular to the plane of rotation of rod. Find the emf induced in the rod.

Draw a labelled diagram of a step-up transformer. State the principle on which it works and obtain the ratio of secondary voltage to primary voltage in terms of number of turns and currents in the two coils.

The ratio of the number of turns in the primary to the secondary of an ideal transformer is \(1:5\). If \(5\) kW power at \(200\) V is supplied to the primary, find
(i) current in the primary, and
(ii) output voltage.

Three point charges $2q$, $-2q$ and $q$ are kept at the vertices of an equilateral triangle of side $l$. The potential energy of the system is

Two metal spheres of radii $r_1$ and $r_2$ having charges $q_1$ and $q_2$ are brought in contact. Which statement is NOT correct?

An electric dipole consists of two point charges \(+q\) and \(-q\) separated by a distance \(2a\). Derive an expression for the electric field \(\vec E\) due to this dipole at a point distant \(r\) from the centre of the dipole on the equatorial plane. Write the expression for the electric field at a far off point, i.e. \(r \gg a\).

A dipole is placed in x-y plane such that charges \(+q\) and \(-q\) are located at \(x=a\) and \(x=b\) respectively. There exists an electric field \[ \vec E = 2\hat{i}\,\frac{N}{C} \] in the region. Calculate the force \(\vec F\) and torque \(\vec \tau\) experienced by the dipole.