Physics - Study Mode

[#1266] A circular plate, a cube and a sphere, all made up of same material and having the same mass, are heated to 300°C and left in a room. Which of them will have the slowest rate of cooling?
Correct Answer

(C) Sphere

Explanation

Solution: In the late of 17th century British scientist Isaac Newton studied cooling of bodies. Experiments showed that the cooling rate is approximately proportional to the difference of temperatures between the heated body and the environment. This fact can be written as the differential relation : dQ dt A T T S= abg, where A is the surface area of the body through which the heat is transferred, T is the temperature of the body, TS is the temperature of the surrounding environment, á is the heat transfer coefficient depending on the geometry of the body, state of the surface, heat transfer mode, and other factors. Surface area or volume ratio is an important influence on temperature control. For same volume sphere has minimum surface area, while circular plate has maximum surface area. So sphere cools slowest and plate cools fastest.

[#1267] The humidity of the air depends upon
Correct Answer

(D) All of the above

Explanation

Solution: The humidity of the air depends upon weather, temperature and location.

[#1268] In a freezer ice cubes will be formed more quickly in trays made of
Correct Answer

(C) Aluminium

Explanation

Solution: Aluminium being a good conductor of heat conducts away the heat from the substance quite easily and causes quick freezing.

[#1269] The ''four stroke petrol engine' is based on
Correct Answer

(B) Otto-cycle

Explanation

Solution: A four-stroke engine (also known as four-cycle) is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine’s crankshaft, and one single thermodynamic cycle. The earliest of these to be developed is the Otto cycle engine developed in 1876 by Nikolaus August Otto in Cologne, Germany, after the operation principle described by Alphonse Beau de Rochas in 1861.

[#1270] The spring balance works on the principle of ________ .
Correct Answer

(B) Hooke's Law

Explanation

Solution: Spring balance works on the principle of Hooke's law. Hooke's law states that the strain of the material is proportional to the applied stress within the elastic limit of that material.