1. Converts electric energy into mechanical energy
2. Converts chemical energy into electric energy
3. Converts mechanical energy into electrical energy
4. Converts electrical every into chemical energy
Option “3” is correct. A dynamo is an electrical generator that produces direct current with the use of a commutator. It converts mechanical energy into electrical energy.
482. Transformer is used for-
1. Converting AC into DC
2. Converting DC into AC
3. To step up DC voltages
4. To step up or step down AC voltages
Option “4” is correct. The transformer is used to step up and step down the alternating current. There are two types of coils in transformers (i) Primary coil (2) Secondary coil. Alternate current flows through the primary coil which inflicts the potential in the secondary coil.
483. A ball rolling along the ground gradually slows down and finally comes to rest is due to ________.
1. Friction
2. Magnetic force
3. Electrostatic force
4. Muscular force
Option “1” is correct. A ball rolling along the ground gradually slows down and finally comes to rest is due to friction.
484. The angle between the __________and the incident ray is called the angle of incidence.
1. Surface
2. Normal
3. Tangent
4. Reflected ray
Option “2” is correct. The angle between the Normal and the incident ray is called the angle of incidence.
485. Who invented the thermos flask?
1. Ray Tomlinson
2. Tim Berners-Lee
3. William Cullen
4. James Dewar
Option “4” is correct. James Dewar was inventor of the thermos flask.
486. Friction is caused by the ______________ on the two surfaces in contact.
1. Roughness
2. Smoothness
3. Densities
4. Gaps
Option “1” is correct. friction was caused due to the roughness of the two surfaces in contact with each other
487. Sun appears red in colour at sunrise and sunset due to –
1. The fact that sun emits only red colour at that time
2. Red light having longer wave length scatters away
3. That sun comes out of the mountains
4. That all other colours scatter away except red
Option “4” is correct. During sunrise and sunset, the rays have to travel a larger part of the atmosphere because they are very close to the horizon. Therefore, light other than red is mostly scattered away. Most of the red light, which is the least scattered, enters our eyes. Hence, the sun and the sky appear red.
488. At hill stations, the boiling point of water will be –
1. Same as at sea level
2. less than that at sea level
3. more than that at sea level
4. Equal to the melting point of ice
Option “2” is correct. At hill stations, the boiling point of water will be less than that at sea level due to change in atmospheric pressure.
489. The component used for tuning a radio is basically a variable ___________.
