Tag: light year

Questions Related to light year

Which of the following is the smallest unit of distance?

physics constellations and galaxies light year evolution and end stages of stars in the world of stars

  1. light year

  2. parsec

  3. astronomical unit

  4. km

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Correct Option: D
Explanation:

Out of these four units kilometer is the smallest unit.

The nearest star to the Earth (apart from the Sun) is 'alpha centauri' which is about .......... away form the Earth

physics constellations and galaxies light year evolution and end stages of stars in the world of stars

  1. 4.3 light years

  2. 3.26 light years

  3. $4.3 \times 10^{12}$ km

  4. $3.26 \times 10^{15}$ km

Show answer
Correct Option: A
Explanation:

Alpha century is a star system closest to earth other than sun. Its distance from the earth is about $4.367$ light years.

One light year is equal to _________.

physics constellations and galaxies light year evolution and end stages of stars in the world of stars

  1. $3.26$ parsec

  2. $3.26$ km

  3. $3.26$ AU

  4. $\cfrac{1}{3.26}$ parsec

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Correct Option: D
Explanation:

1 light year = $\dfrac { 1 }{ 3.26 } $ parsec

Velocity of light is

physics constellations and galaxies light year evolution and end stages of stars in the world of stars

  1. $3\times 10^4km/s$

  2. $3\times 10^6km/s$

  3. $3\times 10^5km/s$

  4. $3\times 10^3km/s$

Show answer
Correct Option: C
Explanation:

Ans : $3\times { 10 }^{ 5 }km/s$

The average distance between Earth and the Sun is $1.496\times {10}^{8}\ km$ and the speed of light coming from the Sun is $3\times {10}^{8}\ m/s$. How much time will it take for Sun's rays to reach Earth?

physics constellations and galaxies light year evolution and end stages of stars in the world of stars

  1. $3\ min$

  2. $498.66\ s$

  3. $8\ min$ $30\ s$ 

  4. $554\ s$

Show answer
Correct Option: B
Explanation:

Distance between Earth and Sun$=1.496\times {10}^{8}\ km=1.496\times {10}^{11}\ m$
Speed of light $=3\times {10}^{8}\ m/s$
By using the formula:
$speed=\cfrac{Distance}{Time}$
or $3\times {10}^{8}\ m/s=\cfrac{1.496\times {10}^{11}m}{Time}$
So,  $Time=\cfrac{1.496\times {10}^{11}\ m}{3\times {10}^{8}\ m/s}$ = $\cfrac{1496}{3}s$ $=498.66\ s$ 

If light travelling from the Sun at the speed of $3\times {10}^{8}\ m/s$, reach a planet $A$ in $25\ min\  30\ sec$. Then what is the distance between the Sun and the planet? 

(1 light year $=9.461\times {10}^{12}\ km$)

physics constellations and galaxies light year evolution and end stages of stars in the world of stars

  1. $3$ light minutes

  2. $0.48\times {10}^{-4}$ light year

  3. $1.96\times {10}^{4} $light year

  4. $2.5$ light years

Show answer
Correct Option: B
Explanation:

Speed of light $=3\times {10}^{8}\ m/s$
Time taken $=25\ min\ 30\ sec = 1530\ sec$
By using the formula, 
$Speed=\cfrac{Distance}{Time}$
or 

$Distance=Speed \times Time$ $=3\times {10}^{8}\times 1530$ $=4590\times {10}^{8}\ m$ $=4590\times {10}^{5}\ km$
Distance (in light year) $=\cfrac{4590\times {10}^{5}}{9.461\times {10}^{12}}$ $=0.48\times {10}^{-4}$ light year.

If the light from star $A$ takes $15$ min to reach star $B$ and the speed of light is $3\times {10}^{8}m/s$, then what is the distance between the stars?

physics constellations and galaxies light year evolution and end stages of stars in the world of stars

  1. $2.7\times {10}^{8}km$

  2. $2,9\times {10}^{11}km$

  3. $2.7\times {10}^{8}m$

  4. $36\times {10}^{9}km$

Show answer
Correct Option: A
Explanation:

Given $t=15$min
Speed of light $=3\times {10}^{8}m/s$
$\therefore$ $t=15min=15\times 60=900 sec$
By using the formula
$Speed=\cfrac{Distance}{Time}$
$Distance=Speed \times time$ $=3\times {10}^{8}m/s\times 900 sec$ $=2700\times {10}^{8}m$ $=2.7\times {10}^{8}km$

How does astronomer calculate distance of star?

physics constellations and galaxies light year evolution and end stages of stars in the world of stars

  1. Comparing apparent brightness of star to true brightness

  2. Comparing true brightness of star to apparent brightness

  3. Comparing true brightness of star to true brightness

  4. None

Show answer
Correct Option: A
Explanation:

The brightness of the stars changes over time. The difference in the brightness (difference in the apparent brightness to the true brightness) over the time allows calculating the distance to the star. This is the cepheid variable stars method that is used to measure the distance to stars beyond 100 light years.

Comparing the apparent brightness of the star to true brightness