Physics

261. Spherical mirror formula relating an object distance ‘u’, image distan

Spherical mirror formula relating an object distance ‘u’, image distance ‘v’ and focal length of mirror ‘f’ may be applied to a plane mirror when

[amp_mcq option1=”focal length goes to infinity.” option2=”focal length goes to zero.” option3=”image distance goes to zero.” option4=”image distance goes to infinity.” correct=”option1″]

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The correct answer is A) focal length goes to infinity.
A plane mirror can be considered a spherical mirror with an infinitely large radius of curvature. Since the focal length of a spherical mirror is half its radius of curvature (f = R/2), the focal length of a plane mirror is also infinite.
The spherical mirror formula is 1/u + 1/v = 1/f. If f goes to infinity, then 1/f goes to zero. The formula becomes 1/u + 1/v = 0, which implies v = -u. This relationship (image distance is the negative of object distance, indicating a virtual image at the same distance behind the mirror as the object is in front) is consistent with the properties of a plane mirror.

262. Power of a lens of focal length 25 cm is

Power of a lens of focal length 25 cm is

[amp_mcq option1=”+2-5 Dioptre” option2=”+3 Dioptre” option3=”+4 Dioptre” option4=”+5 Dioptre” correct=”option3″]

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The correct answer is C) +4 Dioptre.
The power of a lens (P) is defined as the reciprocal of its focal length (f), when the focal length is expressed in meters. The formula is P = 1/f.
Given focal length f = 25 cm. Convert this to meters: 25 cm = 0.25 m.
Power P = 1 / 0.25 m = 1 / (1/4) m = 4 Dioptre (D).
A positive power indicates a converging (convex) lens.

263. Twinkling of stars is primarily due to the atmospheric

Twinkling of stars is primarily due to the atmospheric

[amp_mcq option1=”refraction” option2=”reflection” option3=”polarization” option4=”dispersion” correct=”option1″]

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The correct answer is A) refraction.
Twinkling of stars is caused by atmospheric refraction. As starlight passes through different layers of the Earth’s atmosphere with varying densities and temperatures, it undergoes repeated refraction in random directions, causing the apparent position and brightness of the star to fluctuate.
Planets, being much closer than stars, appear as extended sources rather than point sources. The total amount of light entering the eye from a planet remains relatively constant despite atmospheric refraction, which is why planets do not appear to twinkle.

264. Tyndall effect is a phenomenon of

Tyndall effect is a phenomenon of

[amp_mcq option1=”scattering of light by the colloidal particles.” option2=”refraction of light by the colloidal particles.” option3=”dispersion of light by dust particles.” option4=”refraction of light by dust particles.” correct=”option1″]

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The correct answer is A) scattering of light by the colloidal particles.
The Tyndall effect is the scattering of light as a light beam passes through a colloid. The individual suspension particles scatter and reflect light, making the beam visible.
This phenomenon is exhibited by colloidal solutions and fine suspensions, but not by true solutions. It is used to distinguish between a true solution and a colloidal solution. While dust particles can also scatter light, the term Tyndall effect is specifically associated with scattering by colloidal particles.

265. Myopia is a defect in human vision where an image of a

Myopia is a defect in human vision where an image of a

[amp_mcq option1=”nearby object is focused beyond the retina.” option2=”nearby object is focused before the retina.” option3=”distant object is focused before the retina.” option4=”distant object is focused beyond the retina.” correct=”option3″]

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The correct answer is C) distant object is focused before the retina.
Myopia, or nearsightedness, is a refractive error where light from distant objects is focused in front of the retina instead of directly on it. This results in distant objects appearing blurred.
In myopia, nearby objects are typically focused correctly on the retina (or even slightly behind, requiring less accommodation effort compared to a normal eye), which is why nearby vision is usually clear. Hyperopia (farsightedness) is when light is focused behind the retina.

266. The device used to produce electric current is known as

The device used to produce electric current is known as

[amp_mcq option1=”motor” option2=”generator” option3=”ammeter” option4=”galvanometer” correct=”option2″]

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The correct answer is B) generator.
A generator is a device that converts mechanical energy into electrical energy, thereby producing electric current.
A motor converts electrical energy into mechanical energy. An ammeter is used to measure electric current. A galvanometer is used to detect or measure small electric currents.

267. Imagine a current-carrying straight conductor with magnetic field of l

Imagine a current-carrying straight conductor with magnetic field of lines in anti-clockwise direction. Then the direction of current is determined by

[amp_mcq option1=”the Right-Hand Thumb rule and it would be in the downward direction.” option2=”the Left-Hand Thumb rule and it would be in the downward direction.” option3=”the Right-Hand Thumb rule and it would be in the upward direction.” option4=”the Left-Hand Thumb rule and it would be in the upward direction.” correct=”option3″]

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The direction of the magnetic field around a straight current-carrying conductor is determined by the Right-Hand Thumb Rule (also known as Ampere’s Right-Hand Rule). According to this rule, if you point the thumb of your right hand in the direction of the conventional current, your fingers curl in the direction of the magnetic field lines around the wire. The question states the magnetic field lines are in an anti-clockwise direction when viewed from a certain perspective (presumably from above the conductor). If the current were downwards, using the right-hand rule, your fingers would curl clockwise. If the current were upwards, your fingers would curl anti-clockwise. Since the magnetic field is anti-clockwise, the current must be in the upward direction, and the rule used is the Right-Hand Thumb rule.
The Right-Hand Thumb Rule for a straight conductor states: Point your right thumb in the direction of the conventional current. Your fingers curl in the direction of the magnetic field. An anti-clockwise magnetic field (when looking down onto the wire) implies the current is flowing upwards.
The Left-Hand Rule is typically used in contexts involving forces on current-carrying conductors in magnetic fields (Fleming’s Left-Hand Rule) or for the direction of force on a moving charge in a magnetic field. For determining the direction of the magnetic field created by a current, the Right-Hand Rule is used.

268. Rutherford’s alpha-particle ($\alpha$) scattering experiment was respo

Rutherford’s alpha-particle ($\alpha$) scattering experiment was responsible for the discovery of which one of the following ?

[amp_mcq option1=”Electron” option2=”Proton” option3=”Atomic Nucleus” option4=”Neutron” correct=”option3″]

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Rutherford’s alpha-particle scattering experiment, also known as the Gold Foil experiment, involved firing alpha particles at a thin sheet of gold foil. Most of the alpha particles passed straight through the foil, some were deflected at small angles, and a very small number were deflected at large angles or even bounced back. These observations led Rutherford to propose the existence of a small, dense, positively charged core at the center of the atom, which he called the nucleus. This experiment was a crucial step in understanding the structure of the atom, replacing Thomson’s plum pudding model.
The key finding was that the atom’s positive charge and most of its mass are concentrated in a tiny volume at the center, causing the rare but significant deflections of the positively charged alpha particles.
Electrons were discovered by J.J. Thomson using cathode ray tubes. Protons were later identified as the positively charged particles within the nucleus. Neutrons were discovered by James Chadwick in 1932, much later than Rutherford’s experiment (conducted in 1909-1911, model proposed in 1911).

269. Three equal resistors are connected in parallel configuration in a clo

Three equal resistors are connected in parallel configuration in a closed electrical circuit. Then the total resistance in the circuit becomes

[amp_mcq option1=”one-third of the individual resistance.” option2=”two-third of the individual resistance.” option3=”equal to the individual resistance.” option4=”three times of the individual resistance.” correct=”option1″]

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When resistors are connected in parallel, the total resistance is calculated using the formula for parallel resistances. If three equal resistors, each with resistance R, are connected in parallel, the reciprocal of the total resistance ($R_{total}$) is the sum of the reciprocals of the individual resistances: $1/R_{total} = 1/R + 1/R + 1/R = 3/R$. Therefore, $R_{total} = R/3$. The total resistance becomes one-third of the individual resistance.
For ‘n’ equal resistors each of resistance ‘R’ connected in parallel, the total resistance is $R_{total} = R/n$. In this case, n=3, so $R_{total} = R/3$.
In contrast, if the resistors were connected in series, the total resistance would be the sum of the individual resistances: $R_{total} = R + R + R = 3R$. Connecting resistors in parallel decreases the total resistance of the circuit, while connecting them in series increases it.

270. A uniform motion of a car along a circular path experiences

A uniform motion of a car along a circular path experiences

[amp_mcq option1=”a change in speed due to a change in its direction of motion.” option2=”a change in velocity due to a change in its direction of motion.” option3=”a change in momentum due to no change in its direction of motion.” option4=”a constant momentum due to a change in its direction of motion.” correct=”option2″]

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Uniform motion along a circular path means the object moves at a constant speed. However, velocity is a vector quantity, defined by both magnitude (speed) and direction. In circular motion, the direction of motion is constantly changing as the object moves along the curve. Since the direction of motion is changing, the velocity of the car is also continuously changing, even though its speed is constant.
Speed is the magnitude of velocity. In uniform circular motion, speed is constant. Velocity is a vector (speed + direction). The direction of motion is always tangent to the circular path and continuously changes. Therefore, velocity changes. Momentum is mass times velocity (p = mv). Since velocity changes, momentum also changes.
Since the velocity is changing, there is acceleration. This acceleration is called centripetal acceleration, and it is directed towards the center of the circle. It is responsible for changing the direction of the velocity vector. Uniform circular motion is an example of accelerated motion even though the speed is constant.
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