Option “1” is correct. Heat is the amount of energy that flows spontaneously from a warmer object to a cooler one. In SI system, heat energy is measured in joules (J).
462. If the orbit of a planet is an ellipse then what is the point at which the Sun is located called?
1. Centre
2. Circumcentre
3. Incentre
4. Focus
Option “4” is correct. The Sun and the planets move around each other with their center of mass lying at the focus of the elliptical orbits. In other words, if the orbit of a planet is an ellipse then the point at which the Sun is located called Focus.
463. The laws which govern the motion of planets are called ___________________.
Option “2” is correct. Concave and convex are two classes of spherical mirrors. A concave mirror is a spherical mirror in which the reflecting surface and the center of curvature fall on the same side of the mirror. On the other hand, a convex mirror is a spherical mirror in which the reflecting surface and the center of curvature lie on the opposite sides of the mirror.
465. The frictional force exerted by fluids is also called ________.
1. Drag
2. Buoyancy
3. Upthrust
4. Convection
Option “1” is correct. Drag is a kind of frictional force exerted by fluid which opposes the motion of an object through that fluid. Drag force acts in direction opposite to the direction of motion of the object.
466. Which one of the following is a good electrical conductor?
1. Graphite
2. Diamond
3. Peat
4. Charcoal
Option “1” is correct. Graphite is a very good conductor of electricity due to the mobility of the electrons in its outer valence shells.
467. Which of the following pair is incorrect?
1. Hygrometer – Water vapour content of the atmosphere
2. Lactometer – Specific gravity of liquids
3. Anemometer – Speed of the wind
4. Seismograph – Earthquakes
Option “2” is correct. A lactometer is an instrument used to check purity of milk.
468. Diamond does not conduct electricity mainly because –
1. Its structure is very compact
2. It is of crystalline nature
3. There are only carbons atoms present in it
4. No free electrons are present in it
Option “4” is correct. Diamond is a bad conductor of electricity but good conductor of heat. Electricity is conducted in a crystal by electrons that are relatively free. But in diamond, each carbon atom is covalently bonded with four other carbon atoms and there are no free electrons.
469. Why is weightlessness experienced while orbiting the earth in space ships?
1. Inertia
2. Acceleration
3. Zero gravity
4. Orbital motion
Option “3” is correct. Weightlessness experienced while orbiting the earth in space ships is due to Zero gravity.
470. Who invented Television?
1. J L Baird
2. Aristotle
3. James Clerk Maxwell
4. Nikola Tesla
Option “1” is correct. John Logie Baird was a Scottish engineer, innovator, one of the inventors of the mechanical television, demonstrating the first working television system on 26 January 1926.
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