List of practice Questions

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 ?
Answer the following giving reason :
The assertion that V = IR is a statement of Ohm's law is not true. Why ?
Two cells of emfs 12 V and 6 V are connected in parallel as shown in the figure. Their internal resistances are $1 \, \Omega$ and $0.5 \, \Omega$ respectively. Calculate the emf and internal resistance of the equivalent cell between points A and B.
Define refractive index of a medium in terms of speed of light.
Derive the relation for the refractive index ($\mu$) of a prism in terms of angle of minimum derivation ($\delta_m$) and angle of prism (A).
Acute{}
A ray of light QP is incident normally on the face BC of a triangular prism ABC of refractive index 1.5 kept in air, as shown in the figure. Trace the path of the ray as it passes through the prism and give relevant explanation.
An inductor of $\frac{5}{\pi}$ H, a capacitor of $\frac{50}{\pi}$ $\mu$F and a resistor of $400 \, \Omega$ are connected in series across an ac voltage $v = 140 \sin (100\pi t)$ V. Calculate :
(I) impedance of the circuit, and
(II) rms value of current that flows in the circuit.
(Take $\sqrt{2} = 1.4$)}
Draw a labelled diagram of a step-up transformer. Obtain the ratio of secondary voltage to primary voltage in terms of number of turns in the two coils.
The number of turns in the primary and the secondary coil of an ideal transformer are 100 and 5000 respectively. If 3.3 kW power is supplied to the transformer at 220 V, find (I) current in the primary coil, and (II) output voltage.
Explain the following statement giving reason :
An equipotential surface through a point is normal to the electric field at that point.
Explain the following statement giving reason :
When a dielectric is placed in an external electric field, the electric field inside the dielectric is less than that outside it.
Explain the following statement giving reason :
The potential difference between the plates of a charged parallel plate capacitor decreases when its plates are brought closer.
Obtain an expression for the work done to dissociate the system of three charges $q$, $-4q$ and $2q$ placed at the vertices A, B and C respectively of an equilateral triangle of side '$a$'.
Define the terms (I) resonant frequency, and (II) power factor of a series LCR circuit. For what value of the power factor will the power dissipated in the circuit be maximum ?
Two coils, one of radius $0.5\text{ cm}$ having $10$ turns and the other of radius $5\text{ cm}$ having $50$ turns are placed coaxially in air such that their centres are coincident. Calculate the magnetic flux through the smaller coil if the larger coil carries a current of $3\text{ A}$.
Two coils, one of radius $0.5\text{ cm}$ having $10$ turns and the other of radius $5\text{ cm}$ having $50$ turns are placed coaxially in air such that their centres are coincident. Calculate the mutual inductance of the two coils.
The figure given below shows three straight long parallel conductors kept in x-y plane, carrying currents 2I, I and 3I respectively as shown in figure. Find the magnitude and direction of net magnetic force acting on unit length of conductor 1, due to conductors 2 and 3.
A rectangular loop of sides $l$ and $b$ and resistance ‘R’ is kept in a region in which the magnetic field varies as $B = B_0 \sin \omega t$. Derive expression for the emf induced in the loop.
A rectangular loop of sides $l$ and $b$ and resistance ‘R’ is kept in a region in which the magnetic field varies as $B = B_0 \sin \omega t$. Find the effective value of current that flows in the loop.
What are X-rays ? How are they produced ? Give two uses of X-rays.
Distinguish between isotopes and isobars, giving one example for each.
Derive the relation between atomic mass unit (u) and electron volt (eV).
‘Current is a scalar quantity, although we represent current with an arrow.’ Explain.
Derive the balance condition of a Wheatstone Bridge.