Advertisements
Advertisements
प्रश्न
A LASER is a source of very intense, monochromatic, and unidirectional beam of light. These properties of a laser light can be exploited to measure long distances. The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon’s surface. How much is the radius of the lunar orbit around the Earth?
Advertisements
उत्तर १
Time taken by the laser beam to return to Earth after reflection from the Moon = 2.56 s
Speed of light = 3 × 108 m/s
Time taken by the laser beam to reach Moon = `1/2 xx 2.56 = 1.28 s`
Radius of the lunar orbit = Distance between the Earth and the Moon = 1.28 × 3 × 108 = 3.84 × 108 m = 3.84 × 105 km
उत्तर २
We known that speed of laser light = c = 3 x 108 m/s. If d be the distance of Moon from the earth, the time taken by laser signal to return after reflection at the Moon’s surface
t =2.56 s = `(2d)/c = (2d)/(3xx10^8 ms^(-1))`
`=> d = 1/2 xx 2.56 xx 3 xx 10^(8) m = 3.84 xx 10^8 m`
संबंधित प्रश्न
How many significant figures are present in the 5005?
How many significant figures should be present in the answer of the following calculation?
5 × 5.364
The relative density of lead is 11.3. Its density is ______ g cm–3or ______ kg m–3.
The mean diameter of a thin brass rod is to be measured by vernier callipers. Why is a set of 100 measurements of the diameter expected to yield a more reliable estimate than a set of 5 measurements only?
The photograph of a house occupies an area of 1.75 cm2on a 35 mm slide. The slide is projected on to a screen, and the area of the house on the screen is 1.55 m2. What is the linear magnification of the projector-screen arrangement?
The mass of a box measured by a grocer’s balance is 2.300 kg. Two gold pieces of masses 20.15 g and 20.17 g are added to the box. What is
- What is the total mass of the box?
- What is the difference in the masses of the pieces to correct significant figures?
Precise measurements of physical quantities are a need of science. For example, to ascertain the speed of an aircraft, one must have an accurate method to find its positions at closely separated instants of time. This was the actual motivation behind the discovery of radar in World War II. Think of different examples in modern science where precise measurements of length, time, mass etc. are needed. Also, wherever you can, give a quantitative idea of the precision needed.
A SONAR (sound navigation and ranging) uses ultrasonic waves to detect and locate objects under water. In a submarine equipped with a SONAR the time delay between generation of a probe wave and the reception of its echo after reflection from an enemy submarine is found to be 77.0 s. What is the distance of the enemy submarine? (Speed of sound in water = 1450 m s–1).
State the number of significant figures in the following:
0.2370 g cm–3
State the number of significant figures in the following:
6.032 N m–2
State the number of significant figures in the following:
0.0006032 m2
The radius of the circle is 3.12 m. Calculate the area of the circle with regard to significant figures.
The sum of the numbers 436.32, 227.2 and 0.301 in appropriate significant figures is ______.
Calculate the length of the arc of a circle of radius 31.0 cm which subtends an angle of `pi/6` at the centre.
Significant figures in a measurement include which of the following?
Which of the following measurements has exactly two significant figures?
Which of the following measurements contains exactly two significant figures?
