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Atul came to know from his father that pole star is the only star in the sky that does not move as the night passes. But his father did not tell him the reason. Can you help him?

Stars appear moving because of earth's rotation. But pole star is located in direction of earth's axis. So there is no effect of rotation on the... View Article

A N-typesemiconductor is [AFMC 1988; RPMT 1999]

N-type semiconductors are neutral because neutral atoms are added during doping. ... View Article

What is the principle behind ocean thermal energy?Statement1: The warm water at surface is used to boil ammonia , which vaporizes and then used to rotate turbine. Statement 2: the ammonia is vaporized as only then it gains sufficient kinetic energy for power generation.

The water at the surface of the sea or ocean is heated by the Sun while the water in deeper sections is relatively cold. This difference in... View Article

Light year is the unit of distance. It is the distance travelled by light in one year. If the speed of light is equal to 3×108 m/s , how many kilo-meters will make up 1 light year?

1 Light year = speed x time = 3 x 108 m/s x 365 x 24 x 60 x 60 s = 9.46 x 1015 m = 9.46 x 1012 km... View Article

Alternating current can not be measured by dc ammeter because

In dc ammeter, a coil is free to rotate in the magnetic field of a fixed magnet.If an alternating current is passed through such a... View Article

Tarun got to know from his elder brother that sun is the nearest star and is approximately 150 million kilometers away from the earth. He wanted to know which is the next nearest star and what is its distance from the earth. His tutor told him that the nearest star is proxima centauri and is at a distance of 4.3 light years from the earth. Tarun does not know what a light year is. Can you tell him?

One light year is the distance travelled by the light in one year.... View Article

The reading of ammeter in the circuit shown will be

Given XL = XC = 5Ω this is the condition of resonance. Since VL = VC net voltage across L and C combination will be zero. Voltage... View Article

Sun is also a star but it looks larger than other stars. Why?

Sun is also a star but it looks larger than other stars because other stars are millions of times farther away than sun.The largest known star in... View Article

A bulb and a capacitor are connected in series to a source of alternating current. If its frequency is increased, while keeping the voltage of the source constant, then

When a bulb and a capacitor are connected in series to an ac source, then on increasing the frequency the current in the circuit is increased,... View Article

Why can’t we easily see stars and planets in the sky when we are in a city but can easily see them elsewhere?

Due to pollution, there are many particles in the air, which absorb the light coming from the distant stars and planets. And that is why, the... View Article

Rahul had gone to his village in summer vacation. After dinner, he went on the roof with his cousin. He saw countless bright objects in the sky. His mother had told him that the bright objects that twinkle in the sky are called stars. But he saw a few objects that were bright but they were not twinkling. What were they?

The bright objects which are not shining were planets.... View Article

Which of these options look similar to the constellation Cassiopeia?

Cassiopeia looks like a distorted letter W or M... View Article

If A and B are identical bulbs which bulbs glows brighter

(XC) >> (XL) As the impedance is more in capacitor, bulb B will be glows less brighter compared to Bulb A... View Article

Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.

The air gets trapped between two layers of warm clothes. Air acts as insulator of heat. This layer prevents our body heat to escape in the... View Article

Following figure shows an ac generator connected to a “block box” through a pair of terminals. The box contains possible R, L, C or their combination, whose elements and arrangements are not known to us. Measurements outside the box reveals that e = 75 sin (sin omega t) volt, i = 1.5 sin ( omega t + 45o) amp then, the wrong statement is

Since voltage is lagging behind the current, so there must be no inductor in the box. ... View Article

The vector diagram of current and voltage for a circuit is as shown. The components of the circuit will be 635056321029926369_6005818.PNG

From phasor diagram it is clear that current is lagging with respect to Erms. This may be happen in LCR or LR circuit. ... View Article

Sam’s father and mother are astronauts. Last month they returned from a tour to moon. Sam’s father told him that they had air filled helmet and it also had microphone, which they used for talking to each other. But his mother was not able to listen to him when they opened their helmets. (Assume they were wearing oxygen masks when they opened their helmets). What is the reason?

There is no atmosphere on the moon. Sound needs a medium to travel and since there is no air, sound cannot travel. So his mother was not able to... View Article

Choose the correct option. Statement 1: The shape of the moon changes everyday and the various shapes seen during a month are called phases of the moon. Statement 2: Moon has no light of its own. We see only that part of moon, which reflects light of the sun to us. The position of moon changes due to its revolution around earth and hence the portion of moon reflecting the light of sun to us.

The moon does not produce its own light, whereas the Sun and other stars do. We see the moon because the sunlight falling on the moon gets... View Article

The first law of Motion is also known as Gallileo’s law of inertia.

Newton’s First Law of motion states that a body at rest will remain at rest and body at motion will remain in uniform motion unless an... View Article

If a ray of light falls along the normal of a plane mirror, then the light ray will reflect back at angle of

According to the first law of reflection, the angle of incidence should be equal to the angle of reflection, so if a light ray falls at an angle... View Article

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