Physics Exam Prep
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Physics Exam Prep
Sample questions with model answers
Every question in the paper gets a full exam-length answer in the app — organised by marks, the way a topper writes it.
A cube of side 0.1 m is placed, as shown in the figure, in a region where electric field \(\vec{E} = 500 x \hat{i}\) exists. Here x is in meters and E in NC⁻¹. Calculate: (a) the flux passing through the cube, and (b) the charge within the cube.
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Use \(\Phi = \int \vec{E} \cdot d\vec{A}\) for flux and \(Q = \epsilon_0 \Phi\) for charge.
The full exam-length answer is in the app.
A proton with kinetic energy \(1.3384 \times 10^{-14}\) J moving horizontally from north to south, enters a uniform magnetic field B of 2.0 mT directed eastward. Calculate: (a) the speed of the proton (b) the magnitude of acceleration of the proton (c) the radius of the path traced by the proton [Take (q/m) for proton = \(1.0 \times 10^8\) C/kg]
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Speed = \(\sqrt{\frac{2K}{m}}\), radius = \(\frac{mv}{qB}\).
The full exam-length answer is in the app.
An inductor, a capacitor and a resistor are connected in series with an ac source \(v = v_m \sin \omega t\). Derive an expression for the average power dissipated in the circuit. Also obtain the expression for the resonant frequency of the circuit.
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Average power \(P_{avg} = \frac{V_{rms}^2}{R}\) and resonant frequency \(f_0 = \frac{1}{2\pi\sqrt{LC}}\).
The full exam-length answer is in the app.
Define 'current density'. Is it a scalar or a vector? An electric field \(\vec{E}\) is maintained in a metallic conductor. If n be the number of electrons (mass m, charge -e) per unit volume in the conductor and \(\tau\) its relaxation time, show that the current density \(\vec{j} = \alpha \vec{E}\), where \(\alpha = \frac{ne^2\tau}{m}\).
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Current density \(\vec{j} = n e \vec{v}\), where \(\vec{v}\) is drift velocity.
The full exam-length answer is in the app.
What is a Wheatstone bridge? Obtain the necessary conditions under which the Wheatstone bridge is balanced.
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A Wheatstone bridge is a circuit used to measure unknown resistances; it is balanced when \(\frac{R_1}{R_2} = \frac{R_3}{R_4}\).
The full exam-length answer is in the app.
(a) "The wavelength of the electromagnetic wave is often correlated with the characteristic size of the system that radiates." Give two examples to justify this statement. (b) (i) Long distance radio broadcasts use short-wave bands. Why? (ii) Optical and radio telescopes are built on the ground, but X-ray astronomy is possible only from satellites orbiting the Earth. Why?
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Examples include radio waves for long distances and X-rays for high-energy processes.
The full exam-length answer is in the app.
Write the drawbacks of Rutherford's atomic model. How did Bohr remove them? Show that different orbits in Bohr's atom are not equally spaced.
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Drawbacks include instability of electrons; Bohr introduced quantized orbits with \(r_n \propto n^2\).
The full exam-length answer is in the app.
(a) State any two properties of a nucleus. (b) Why is the density of a nucleus much more than that of an atom? (c) Show that the density of the nuclear matter is the same for all nuclei.
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Nuclear density is high due to compact packing of nucleons; density is consistent across elements.
The full exam-length answer is in the app.
Three point charges Q1, Q2 and Q3 are located in x-y plane at points (-d, 0), (0, 0) and (d, 0) respectively. Q1 and Q3 are identical and Q2 is positive. What will be the nature and value of Q1 so that the potential energy of the system is zero?
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Set potential energy to zero by balancing charges: Q1 = -Q2.
The full exam-length answer is in the app.
A bar magnet of magnetic moment \(2.5 \text{ JT}^{-1}\) lies aligned with the direction of a uniform magnetic field of 0.32 T. (a) Find the amount of work done to turn the magnet so as to align its magnetic moment (i) normal to the field direction, and (ii) opposite to the field direction. (b) What is the torque on the magnet in above cases (i) and (ii)?
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Work done \(W = -\vec{\mu} \cdot \vec{B}\); torque \(\tau = \vec{\mu} \times \vec{B}\).
The full exam-length answer is in the app.
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