List of practice Questions

A 5 cm long pencil is placed along the principal axis of a concave mirror of focal length 20 cm such that its nearest end is at a distance of 25 cm from the mirror. Calculate the length of the image of the pencil.
In a Young’s double-slit experiment, a beam of light consisting of two wavelengths 500 nm and 600 nm is used. The interference fringes are observed at a screen placed 1.8 m away from the plane of slits (slit separation 0.3 mm). Calculate the least distance from the central maximum where the bright fringes due to both the wavelengths coincide.
Calculate the temperature at which the resistance of a conductor becomes 20% more than its resistance at $27^\circ\text{C}$. The value of the temperature coefficient of resistance of the material of conductor is $2.0 \times 10^{-4} ^\circ\text{C}^{-1}$.
A ray of light is incident on the face of a triangular prism of refracting angle $60^\circ$ and it just suffers total internal reflection at the other face. Find the angle of incidence for the ray if the refractive index of the material of the prism is $\sqrt{2}$.
Write two points of difference between intrinsic and extrinsic semiconductors.
A galvanometer of resistance $27 \Omega$ is converted into an ammeter of range (0 – 10 mA) using a resistance of $3 \Omega$. The galvanometer will show full scale deflection for a current of about –
The magnetic flux $\phi$ (in Wb) linked with a coil is related to time t (in s) as
$\phi = 5 At^2 + Bt - 2C$
The SI units of A and B are respectively
The figure shows the variation of capacitive reactance ($X_C$) of two ideal capacitors of capacitances $C_1$ & $C_2$ with the reciprocal of angular frequency ($1/\omega$) of ac source. The value of $C_1/C_2$ is
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 a electric device when connected to a dc source of voltage V is proportional to its resistance.
Assertion (A) : On increasing the intensity of incident light of frequency $\nu$ ($> \nu_0$) on a photosensitive surface, the photocurrent increases.
Reason (R) : The stopping potential for a photosensitive surface increases with increase of frequency $\nu$ ($> \nu_0$) of incident light.
Two metal spheres of radii $r_1$ and $r_2$ ($> r_1$) having charges $q_1$ and $q_2$ respectively kept in air, are brought in contact. Which of the following statements is not correct ?
In Bohr model of hydrogen atom, an electron makes a transition from n = 4 state to n = 1 state and a photon of frequency $\nu$ is emitted. The frequency of photon emitted when an electron makes a transition from n = 4 state to n = 2 state in the same model is
Figure shows a magnet dropped through a small loop with a small cut. Which of the following statements is correct ?
The expression of magnetic fields associated with four electromagnetic waves are given below :
I. $B_1 = (4 \times 10^{-6} \text{ T}) \sin [0.7 \times 10^3 x + 1.4 \times 10^{11} t]$
II. $B_2 = (2 \times 10^{-7} \text{ T}) \sin [0.6 \times 10^3 x + 1.5 \times 10^{11} t]$
III. $B_3 = (3 \times 10^{-5} \text{ T}) \sin [0.5 \times 10^3 x + 1.5 \times 10^{11} t]$
IV. $B_4 = (5 \times 10^{-4} \text{ T}) \sin [0.2 \times 10^4 x + 4.8 \times 10^{11} t]$
Which wave is travelling in free space ?
Which of the following substance has relative magnetic permeability $\mu_r \gg 1$ ?
A straight conductor lies along x-axis and carries a current of 2 A along +x direction. The magnetic field at a point (0, 40 cm, 0) due to 1 cm length of conductor centered at the origin points along.
What is the difference between a ray and a wavefront ?
A plane wave is incident on a reflecting surface. Using Huygens principle, show how it is reflected from the surface. Hence, verify the law of reflection.
Depict refraction of a plane wave by a convex lens.
Three point charges +q, –2q and +q are placed along x-axis at points x = –1 m, x = 0 m and x = 2 m respectively. The potential energy of the system is
A photosensitive surface is illuminated by radiations of wavelength $\lambda_1$, $\lambda_2$ ($>\lambda_1$) and $\lambda_3$ one by one and photoemission is observed in each case. $\lambda_1, \lambda_2$ lies in UV range and $\lambda_3$ in visible range. If $V_1, V_2$ and $V_3$ are stopping potential in these cases respectively, then
In Bohr model of hydrogen atom, the value of potential energy of an electron in nth orbit varies with ‘n’ as
Answer the following giving reason :
The electron drift speed is estimated to be only a few mm/s for currents in the range of a few amperes. How, then, is the current established almost the instant a circuit is closed ?
Answer the following giving reason :
A low voltage supply from which one needs high currents must have very low internal resistance. Why ?