202066 marks18 questions
6 of its 18 questions are here. The rest have a figure or are still being checked, so for now they're only in the official PDF.
Sit this paper against the clock, marked by its official answers, or get a new paper like it. Sign in first; practising is part of Pro.
Source: JEE (Advanced) 2020, Paper 1, Physics, published by JEE (Advanced). The official PDF
A particle of mass m moves in circular orbits with potential energy V(r) = Fr, where F is a positive constant and r is its distance from the origin. Its energies are calculated using the Bohr model. If the radius of the particle’s orbit is denoted by R and its speed and energy are denoted by v and E, respectively, then for the nᵗʰ orbit (here h is the Planck’s constant)
The filament of a light bulb has surface area 64 mm². The filament can be considered as a black body at temperature 2500 K emitting radiation like a point source when viewed from far. At night the light bulb is observed from a distance of 100 m. Assume the pupil of the eyes of the observer to be circular with radius 3 mm. Then (Take Stefan-Boltzmann constant = 5.67 × 10⁻⁸ Wm⁻²K⁻⁴, Wien’s displacement constant = 2.90 × 10⁻³ m-K, Planck’s constant = 6.63 × 10⁻³⁴ Js, speed of light in vacuum = 3.00 × 10⁸ ms⁻¹)
Put a uniform meter scale horizontally on your extended index fingers with the left one at 0.00 cm and the right one at 90.00 cm. When you attempt to move both the fingers slowly towards the center, initially only the left finger slips with respect to the scale and the right finger does not. After some distance, the left finger stops and the right one starts slipping. Then the right finger stops at a distance xR from the center (50.00 cm) of the scale and the left one starts slipping again. This happens because of the difference in the frictional forces on the two fingers. If the coefficients of static and dynamic friction between the fingers and the scale are 0.40 and 0.32, respectively, the value of xR (in cm) is ______.
Consider one mole of helium gas enclosed in a container at initial pressure P₁ and volume V₁. It expands isothermally to volume 4V₁. After this, the gas expands adiabatically and its volume becomes 32V₁. The work done by the gas during isothermal and adiabatic expansion processes are Wiso and Wadia, respectively. If the ratio Wiso/Wadia = f ln2, then f is ________.
A stationary tuning fork is in resonance with an air column in a pipe. If the tuning fork is moved with a speed of 2 ms⁻¹ in front of the open end of the pipe and parallel to it, the length of the pipe should be changed for the resonance to occur with the moving tuning fork. If the speed of sound in air is 320 ms⁻¹, the smallest value of the percentage change required in the length of the pipe is ____________.
A circular disc of radius R carries surface charge density σ(r) = σ₀ (1 − r/R), where σ₀ is a constant and r is the distance from the center of the disc. Electric flux through a large spherical surface that encloses the charged disc completely is ϕ₀. Electric flux through another spherical surface of radius R/4 and concentric with the disc is ϕ. Then the ratio ϕ₀/ϕ is_________.