Physics Basics — Set 3
Physics · भौतिकी की मूल बातें · Questions 21–30 of 50
Which law states that energy cannot be created or destroyed, only transformed?
Correct Answer: A. Law of Conservation of Energy
The Law of Conservation of Energy states that the total energy of an isolated system remains constant. Energy can change from one form, like potential, to another, like kinetic. This principle is a fundamental pillar of thermodynamics and mechanics.
Which instrument is used to detect and measure small electric currents?
Correct Answer: B. Galvanometer
A galvanometer is an electromechanical instrument used for detecting and indicating an electric current. It works by deflecting a needle in response to a magnetic field produced by the current. It is highly sensitive and can detect currents of very low magnitude.
Who discovered the phenomenon of Radioactivity?
Correct Answer: B. Henri Becquerel
Henri Becquerel discovered radioactivity in 1896 while studying phosphorescent materials. He found that uranium salts emitted rays that could penetrate opaque paper. He shared the Nobel Prize in Physics with Marie and Pierre Curie for this discovery.
The unit 'Light Year' measures which of the following?
Correct Answer: A. Distance
A light-year is the distance that light travels in a vacuum in one Julian year. It is equivalent to about 9.46 trillion kilometers. Astronomers use this unit to describe the vast distances between stars and galaxies.
Which of these devices converts mechanical energy into electrical energy?
Correct Answer: C. Dynamo
A dynamo is a generator that produces direct current using electromagnetic induction. It converts the mechanical rotation of a coil into electrical energy. Michael Faraday's principles of induction are the basis for this device's operation.
Which subatomic particle has a positive electric charge?
Correct Answer: B. Proton
The proton is a subatomic particle found in the nucleus of every atom with a positive charge. The number of protons in an atom determines its chemical element. Ernest Rutherford is credited with the discovery of the proton.
What is the unit of measure for the 'Power' of a lens?
Correct Answer: A. Dioptre
The power of a lens is measured in dioptres, which is the reciprocal of the focal length in meters. A converging lens has a positive dioptre value, while a diverging lens has a negative one. This unit is commonly used by optometrists to prescribe corrective glasses.
Who invented the first practical Telephone?
Correct Answer: B. Alexander Graham Bell
Alexander Graham Bell was awarded the first U.S. patent for the telephone in 1876. His invention revolutionized global communication by allowing the transmission of sound over wires. He co-founded the American Telephone and Telegraph Company (AT&T).
What is the boiling point of pure water at standard sea-level pressure in Celsius?
Correct Answer: A. 100°C
At standard atmospheric pressure, pure water boils at exactly 100 degrees Celsius. This value is used as a fixed point for calibrating the Celsius temperature scale. The boiling point decreases as the altitude increases due to lower atmospheric pressure.
Which instrument is used to measure the depth of the ocean?
Correct Answer: B. Fathometer
A fathometer is a device used to determine the depth of water by transmitting sound waves. It calculates depth based on the time it takes for the echo to return from the ocean floor. This technique is commonly known as echo sounding.