NEET 2019 — Physics

When a block of mass $M$ is suspended by a long wire of length $L$, the length of the wire becomes $(L+l)$. The elastic potential energy stored in the extended wire is:

A mass $m$ is attached to a thin wire and whirled in a vertical circle. The wire is most likely to break when:

Ionised hydrogen atoms and $\alpha$-particles with the same momenta enter a constant magnetic field $B$ at right angles to it. The ratio of the radii of their circular paths $r_H:r_{\alpha }$ will be:

Body A of mass $4m$ moving with speed $u$ collides with another body B of mass $2m$, at rest. The collision is head-on and elastic in nature. After the collision, the fraction of energy lost by body A is:

In a double-slit experiment, when light of wavelength 400 nm was used, the angular width of the first minimum formed on a screen placed 1 m away was found to be $0.2^{\circ }$. What will be the angular width of the first minimum if the entire experimental apparatus is immersed in water (${\mu }_w=4/3$)?

A soap bubble, having a radius of 1 mm, is blown from a detergent solution having a surface tension of $2.5\times 10^{-2}N/m$. The excess pressure inside the bubble equals the pressure at a point $Z_0$ below the free surface of water in a container. Taking $g=10m/{\mathrm{s}}^2$ and density of water $=10^{3}kg/{\mathrm{m}}^3$, the value of $Z_0$ is:

Which colour of light has the longest wavelength?

A disc of radius 2 m and mass 100 kg rolls on a horizontal floor. Its centre of mass has a speed of 20 cm/s. How much work is needed to stop it?

The displacement of a particle executing simple harmonic motion is given by $y=A_0+A\sin \omega t+B\cos \omega t$. Then the amplitude of its oscillation is given by:

Two similar thin equiconvex lenses, of focal length $f$ each, are kept coaxially in contact with each other such that the focal length of the combination is $F_1$. When the space between the two lenses is filled with glycerine (which has the same refractive index, $\mu =1.5$, as the glass) then the equivalent focal length is $F_2$. The ratio $F_1:F_2$ will be:

An increase in the temperature of a gas filled in a container would lead to:

An electron is accelerated through a potential difference of 10,000 V. Its de Broglie wavelength is, nearly: ($m_e=9\times 10^{-31}$ kg)

A copper rod of length 88 cm and an aluminium rod of unknown length have their increase in length independent of the increase in temperature. The length of the aluminium rod is: (${\alpha }_{Cu}=1.7\times 10^{-5}{\mathrm{K}}^{-1}$ and ${\alpha }_{Al}=2.2\times 10^{-5}{\mathrm{K}}^{-1}$)

Pick the wrong answer in the context of a rainbow.

A body weighs 200 N on the surface of the earth. How much will it weigh half way down to the centre of the earth?

Six similar bulbs, each of resistance $R$, are connected to a DC source of emf $E$ (zero internal resistance) in two groups of three bulbs each, section A and section B, with the three bulbs of each section in parallel with each other and the two sections in series with each other and the source. The ratio of the power consumed by the bulbs when (i) all six are glowing, to when (ii) only two bulbs from section A and one bulb from section B are glowing (the rest disconnected), will be:

For a p-type semiconductor, which of the following statements is true?

The average velocity of a particle executing SHM in one complete vibration is:

The SI unit of thermal conductivity is:

A solid cylinder of mass 2 kg and radius 4 cm is rotating about its axis at the rate of 3 rpm. The torque required to stop it after 2 revolutions is:

A force $F=20+10y$ acts on a particle in the $y$-direction, where $F$ is in newton and $y$ in metre. The work done by this force to move the particle from $y=0$ to $y=1$ m is:

Which of the following acts as a circuit-protecting device?

Circuit 1 has a 10 V source driving current $i_1$ through $a10\Omega$ resistor, with an ideal ammeter $A_1$ in series and an ideal voltmeter $V_1$ connected across the resistor-and-ammeter combination. Circuit 2 has the same 10 V source, $10\Omega$ resistor and current $i_2$, with ideal ammeter $A_2$ in series, but this time ideal voltmeter $V_2$ is connected across the resistor alone (not including the ammeter). The readings of the voltmeters and ammeters will be:

A hollow metal sphere of radius $R$ is uniformly charged. The electric field due to the sphere at a distance $r$ from its centre:

At a point A on the earth's surface the angle of dip is $\delta =+25^{\circ }$. At a point B on the earth's surface the angle of dip is $\delta =-25^{\circ }$. We can interpret that:

The total energy of an electron in an atom in an orbit is $-3.4$ eV. Its kinetic and potential energies are, respectively:

In total internal reflection, when the angle of incidence is equal to the critical angle for a pair of media in contact, what will the angle of refraction be?

The work done to raise a mass $m$ from the surface of the earth to a height $h$, equal to the radius of the earth, is:

When an object is shot from the bottom of a long, smooth inclined plane kept at an angle of $60^{\circ }$ with the horizontal, it can travel a distance $x_1$ along the plane. But when the inclination is decreased to $30^{\circ }$ and the same object is shot with the same velocity, it can travel a distance $x_2$. Then $x_1:x_2$ will be:

An $\alpha$-particle consists of:

The speed of a swimmer in still water is 20 m/s. The speed of river water is 10 m/s and is flowing due east. If he is standing on the south bank and wishes to cross the river along the shortest path, the angle at which he should make his strokes with respect to north is given by:

A particle moving with velocity $\vec{v}$ is acted upon by three forces, represented in magnitude and direction by the three sides of a triangle PQR taken in the same order ($\vec{P}$, $\vec{Q}$, $\vec{R}$ head-to-tail forming a closed triangle). The velocity of the particle will:

Two particles A and B are moving in uniform circular motion in concentric circles of radii $r_A$ and $r_B$ with speeds $v_A$ and $v_B$, respectively. Their time period of rotation is the same. The ratio of the angular speed of A to that of B will be:

A block of mass 10 kg is in contact against the inner wall of a hollow cylindrical drum of radius 1 m. The coefficient of friction between the block and the inner wall of the cylinder is 0.1. The minimum angular velocity needed for the cylinder, rotating about its vertical axis, to keep the block stationary is: ($g=10m/{\mathrm{s}}^2$)

Two parallel infinite line charges with linear charge densities $+\lambda C/m$ and $-\lambda C/m$ are placed at a distance of $2R$ from each other in free space. What is the electric field midway between the two line charges?

Two point charges A and B, having charges $+Q$ and $-Q$ respectively, are placed at a certain distance apart, and the force acting between them is $F$. If 25% of the charge of A is transferred to B, then the force between the charges becomes:

A small hole of cross-sectional area 2 mm${}^2$ is present near the bottom of a fully filled open tank of height 2 m. Taking $g=10m/{\mathrm{s}}^2$, the rate of flow of water through the open hole would be nearly:

In the circuit shown, inputs A and B each control a diode into a common node, which is tied through a resistor $R$ to $+6$ V and also drives an LED (Y) to ground: the node — and the LED, which lights when the node is LOW — is pulled LOW whenever at least one of A, B is LOW (0), and goes HIGH (LED off) only when both A and B are HIGH (1). This gives the truth table A,B $\to$ Y: 0,0 $\to$ 1; 0,1 $\to$ 1; 1,0 $\to$ 1; 1,1 $\to$ 0. The correct Boolean operation represented by this circuit is:

In which of the following processes is heat neither absorbed nor released by a system?

An 800-turn coil of effective area 0.05 m${}^2$ is kept perpendicular to a magnetic field of $5\times 10^{-5}$ T. When the plane of the coil is rotated by $90^{\circ }$ around any of its coplanar axes in 0.1 s, the emf induced in the coil will be:

A particle P moves in a circle of radius 3 m, centred at the origin in the $xy$-plane, with period $T=4$ s. At $t=0$, P is at the topmost point of the circle (maximum $y$-displacement). The $y$-projection of the position vector of P, as a function of time, is:

A parallel plate capacitor of capacitance $20\mu F$ is being charged by a voltage source whose potential is changing at the rate of 3 V/s. The conduction current through the connecting wires, and the displacement current through the plates of the capacitor, would be, respectively:

In an experiment, the percentage errors in the measurement of physical quantities $A$, $B$, $C$ and $D$ are 1%, 2%, 3% and 4% respectively. Then the maximum percentage error in the measurement of $X$, where $X=\frac{A^2{B}^{1/2}}{C^{1/3}{D}^3}$, will be:

A cylindrical conductor of radius $R$ carries a constant current, uniformly distributed over its cross-section. Which of the following best describes the magnitude of the magnetic field $B$ as a function of the distance $d$ from the axis of the conductor?