Physics MCQs

Notes:
The correct answer is Quantum Theory. Black body radiation refers to the electromagnetic radiation emitted by an idealized object that absorbs all incident radiation. Max Planck introduced the concept in 1900, leading to the development of quantum mechanics. This theory explains that energy is quantized, emitted in discrete packets called quanta or photons, resolving the ultraviolet catastrophe predicted by classical physics.

Notes:
When two drops of mercury come into contact, they will tend to merge together and form a single drop with a minimum surface area. This is because of the properties of mercury, which is a liquid metal with a high surface tension. The surface tension of a liquid is a measure of its elasticity, and it is determined by the cohesive forces between the molecules of the liquid. In the case of mercury, the high surface tension causes the molecules at the surface of the liquid to be strongly attracted to each other, which results in the formation of a relatively smooth and spherical surface. When two drops of mercury are brought together, the surface tension causes them to merge and form a single drop with the smallest possible surface area. This phenomenon is known as the “minimization of surface area” and it is a common feature of liquids with high surface tension.

Notes:
The correct answer is that the person hears the sound waves twice: first via steel and then via air. Sound travels faster in solids than in gases. in steel, it travels at about 5,960 m/s, while in air, it travels at approximately 343 m/s. Given the long distance of 700 meters, the sound will reach the person through the steel rail first, followed by the sound traveling through the air. This phenomenon illustrates the differences in sound propagation speeds in different media.

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The range of the tera hertz radiation frequency is from roughly 0.1 THz to 10 THz. It is higher than the frequency of radio waves and microwaves, but lower than the frequency of infrared light.

Notes:
The recoiling of gun is an example of Law of Conservation of Linear Momentum. When gun fires a bullet, it experiences a force in forward direction (action) , as a result the gun exerts a backward force (reaction) on the shoulder. Thus, it is in accordance with Law of Conservation of Linear Momentum which is also the Newton’s 3rd law of motion.

Notes:
Werner Heisenberg, a german Physicist, discovered the Uncertainity principle. As per the uncertainty principle, we cannot measure the position (x) and the momentum (p) of a particle with absolute precision. The more accurately we know one of these values, the less accurately we know the other. It represnts the effects of wave-particle duality on the properties of subatomic objects.

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The unit of impulse is Ns. Impulse = Force(N) x Time(s) Impulse can be defined as the integral of a force, F, over the time interval, t, for which it acts.

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The SI unit of Linear Momentum is kg m/s Linear Momentum = Mass(kg) x Velocity (m/s) Linear Momentum is the quantity of motion of a moving body. Dimensional Formula of Linear Momentum is [M¹ L¹ T^-1]

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Power of lens is measured in dioptre(D). Power of lens = 1/focal length The power of a lens is its ability to bend light. The greater the power the greater the refraction of light.

Notes:
The second law of motion gives us a measure of force. The product of the mass of the body and the acceleration produced in it gives us the magnitude of force. Force (f) = mass (m) x acceleration (a) Force is a vector quantity and the direction is same as that of acceleration