Distance Between Sun and Earth When c = 1 | Class 11 Physics Solution
- Dr.Sanjaykumar Pawar
 |
| When speed of light is taken as 1 unit, distance becomes numerically equal to time in seconds. |
🔗 INTERNAL LINKS
/class-11-physics-units-and-measurement
/class-11-physics-important-numericals
/natural-units-system-physics-explained
/cbse-class-11-physics-short-notes
/physics-tricks-for-exam-preparation
/sun-earth-distance-numericals
CBSE Class 11 Physics - Topper Notes
Question
A new unit of length is chosen such that the speed of light in vacuum is unity. What is the distance between the Sun and the Earth in terms of the new unit if light takes 8 min 20 s to cover this distance?
Solution
Given:
- Speed of light, c = 1 (in new unit system)
- Time = 8 min 20 s
Step 1: Convert time into seconds
8 min 20 s = (8 × 60) + 20 = 480 + 20 = 500 s
Step 2: Use formula
Distance = Speed × Time
Distance = 1 × 500 = 500 units
Final Answer: Distance = 500 units
Short Notes (Exam Revision)
- When speed of light c = 1, units become simplified natural units.
- 1 unit of length = distance travelled by light in 1 second.
- Distance = Speed × Time → here Speed = 1, so Distance = Time.
- Always convert time into seconds before solving.
- This concept is useful in relativity and theoretical physics.
Topper Trick
If c = 1, then simply convert time into seconds → that is the answer!
Practice Questions & Answers (c = 1 System)
Q1.
If speed of light is 1 unit/sec, how much distance does light cover in 15 seconds?
Answer:
Distance = Speed × Time = 1 × 15 = 15 units
Q2.
Light takes 2 minutes to travel a distance. Find the distance in this system.
Answer:
2 minutes = 120 seconds
Distance = 1 × 120 = 120 units
Q3.
A signal takes 45 seconds to reach Earth. Find the distance.
Answer:
Distance = 1 × 45 = 45 units
Q4.
Light takes 5 minutes 30 seconds to travel from a star to Earth. Find distance.
Answer:
5 min 30 sec = (5 × 60) + 30 = 330 seconds
Distance = 1 × 330 = 330 units
Q5.
If distance is 1000 units in this system, how much time does light take?
Answer:
Time = Distance / Speed = 1000 / 1 = 1000 seconds
Q6.
Why does distance become equal to time when c = 1?
Answer:
Because speed of light c = distance / time = 1
So, distance = time (numerically in this unit system)
Q7.
Light takes 8 min 20 sec to travel from Sun to Earth. Find distance.
Answer:
8 min 20 sec = 500 seconds
Distance = 1 × 500 = 500 units
Q8.
A spaceship signal takes 1.5 hours to reach Earth. Find distance.
Answer:
1.5 hours = 1.5 × 3600 = 5400 seconds
Distance = 1 × 5400 = 5400 units
