Which one among the following stars is nearest to the earth?
- A.Sirius
- B.Arcturus
- C.Spica
- D.Proxima Centauri
Correct answer
Explanation
The correct answer is D, Proxima Centauri. Apart from the Sun, Proxima Centauri is the star nearest to the Earth, about 4.24 light years away.
Proxima Centauri is a small, dim red dwarf in the constellation Centaurus and cannot be seen with the naked eye. It belongs to the Alpha Centauri system, whose two brighter stars, Alpha Centauri A and B, lie a little farther away at about 4.37 light years. Light from Proxima takes over four years to reach us, while sunlight takes only about 8 minutes 20 seconds. At least one planet, Proxima b, orbits it within its habitable zone.
A, Sirius, the Dog Star, is the brightest star in the night sky, but it is about 8.6 light years away. B, Arcturus, a bright orange giant in Boötes, is about 37 light years away. C, Spica, the brightest star of Virgo, is roughly 250 light years away.
Exam tip: nearest star is the Sun; next is Proxima Centauri, 4.24 light years; brightest night star is Sirius.
Practice Questions
View allA negative work is done when an applied force F and the corresponding displacement S are
- A.perpendicular to each other.
- B.parallel to each other.
- C.anti-parallel to each other.
- D.equal in magnitude.
Show answer
Work is negative when the force acts opposite to the displacement, because the angle between them is then 180°. Work done is W = F S cos θ, where θ is the angle between the force and the displacement.
Read the full explanation →Which one of the following statements about a satellite orbiting around the Earth is correct ?
- A.Satellite is kept in orbit by remote control from ground station.
- B.Satellite is kept in orbit by retro-rocket and solar energy keeps it moving around the Earth.
- C.Satellite requires energy from solar panels and solid fuels for orbiting.
- D.Satellite does not require any energy for orbiting.
Show answer
Once a satellite is placed in orbit with the right speed, the Earth's gravity keeps it going round without any engine.
Read the full explanation →Which one of the following is not a conservative force ?
- A.Frictional force
- B.Electric force
- C.Gravitational force
- D.Spring force
Show answer
Friction is a non-conservative force because the work it does depends on the path taken and the energy it removes is lost as heat.
Read the full explanation →A microphone converts
- A.electrical signals to sound waves
- B.sound waves to electrical signals
- C.microwaves to sound waves
- D.sound waves to microwaves
Show answer
A microphone is a transducer that changes the pressure variations of sound into a matching electrical signal. In a common dynamic microphone, sound waves make a thin diaphragm vibrate.
Read the full explanation →When a light ray passes through from air to water with a non-zero angle the ray will be
- A.bending towards the normal
- B.bending away from the normal
- C.propagating in straight line
- D.reflected towards the opposite direction
Show answer
Light slows down when it enters water from air, so a ray that strikes the surface at an angle bends towards the normal.
Read the full explanation →