JEE Main entrance exam Question Bank Solutions for Physics (JEE Main)

A slab consist of two parallel layers of copper and brass of the same thickness and having thermal conductivities in the ratio 1 : 4. If the free face of brass is at 100°C and that of copper at 0°C, the temperature of interface is ______.

A ring consisting of two parts ADB and ACB of same conductivity K carries an amount of heat H. The ADB part is now replaced with another metal keeping the temperatures T₁ and T₂ constant. The heat carried increases to 2H. What should be the conductivity of the new ADB part? (Given `"ACB"/"ADB"` = 3)

Two rectangular blocks A and B of different metals have same length and same area of cross-section. They are kept in such a way that their cross-sectional area touch each other. The temperature at one end of A is 100°C and that of B at the other end is 0°C. If the ratio of their thermal conductivity is 1 : 3, then under steady state, the temperature of the junction in contact will be ______.

A thin square steel plate with each side equal to 10 cm is heated by a blacksmith. The rate of radiated energy by the heated plate is 1134 watts. The temperature of the hot steel plate is ______.

(Stefan's constant σ = 5.67 × 10^-8 watt m^-2K^-4 emissivity of the plate = 1)

An electric heater is used in a room with a total wall area of 137 m² to maintain a temperature of +20°C inside it when the outside temperature is -10°C. The walls have three different layers of materials. The innermost layer is of wood of thickness 2.5 cm, the middle layer is of cement of thickness 1.0 cm and the outermost layer is brick of 25.0 cm. The power of the electric heater will be ______ W. Assume that there is no heat loss through the floor and the ceiling. The thermal conductivities of wood, cement, and brick are 0.125, 1.5, and 1.0 watt/m/°C respectively.

As per the given figure, two plates A and B of thermal conductivity K and 2 K are joined together to form a compound plate. The thickness of plates are 4.0 cm and 2.5 cm respectively and the area of cross-section is 120 cm² for each plate. The equivalent thermal conductivity of the compound plate is `(1+5/alpha)`K, then the value of a will be ______.

A charged particle 'q' is shot towards another charged particle 'Q' which is fixed, with a speed 'v'. It approaches 'Q' upto a closest distance r and then returns. If q were given a speed of '2v' the closest distances of approach would be ______.

The same size images are formed by a convex lens when the object is placed at 20 cm or at 10 cm from the lens. The focal length of convex lens is ______ cm.

When monochromatic red light is used instead of blue light in a convex lens, its focal length will ______.

A cylinder of radius R made of material of thermal conductivity K₁ is surrounded by a cylindrical shell of inner radius R and outer radius 3R made of a material of thermal conductivity K₂. The two ends of the combined system are maintained at two different temperatures. What is the effective thermal conductivity of the system?

A capacitor is connected to a 20 V battery through a resistance of 10 Ω. It is found that the potential difference across the capacitor rises to 2 V in 1 µs. The capacitance of the capacitor is ______ µF. Given: In `(10/9)` = 0.105

Wein's constant is 2892 × 10^-6 SI unit and the value of λm for moon is 14.46 micron. The surface temperature of moon is ______.

The aperture of the objective is 24.4 cm. The resolving power of this telescope. If a light of wavelength 2440 Å is used to see the object will be ______.

Wavelength of light used in an optical instrument are λ₁ = 4000 Å and λ₂ = 5000 Å, then ratio of their respective resolving powers (corresponding to λ₁ and λ₂) is ______.

Which of the following is closer to a black body?

According to Newton's law of cooling, the rate of cooling of the body is proportional to (Δθ), where Δθ is the difference between the temperature of the body and the surroundings, and n is equal to ______.

In 5 minutes, a body cools from 75°C to 65°C at a room temperature of 25°C. The temperature of the body at the end of the next 5 minutes is ______°C.

Water from a pipe is coming at a rate of 100 liters per minute. If the radius of the pipe is 5 cm, the Reynolds number for the flow is of the order of ______.

(density of water = 1000 kg/m³, coefficient of viscosity of water = 1 mPa s)

If p is the density and η is the coefficient of viscosity of fluid that flows with a speed v in the pipe of diameter d, the correct formula for Reynolds number R_e is ______.

A wire fixed at the upper end stretches by length l by applying a force F. The work done in stretching is ______.