Value of 'c': Speed of Light

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Jasmine Grover

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Value of c refers to the speed of light photons in a vacuum and measured in SI units of m/s. The value of the velocity of light, or c, is a constant throughout all parts of the universe. This physical constant has a wide range of applications in physics.

Key Terms: Value of c, Light velocity, significance of the speed of light, speed of light, Photon, Velocity, vacuum, Plane


The Speed of Light

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The velocity of light in vacuum is:

The speed of light is equal to 299792458 m/s ≅ 3×108 m/s.

Light velocity can be described in terms of miles per hour (mph) or kilometers per second (km/s). This is-

The speed of light in miles per hour is 186,000 miles per hour.

Light travels at 299792 km/s in air.

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Time Difference can be Significantly Reduced with Speed of Light

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The speed of light in space is unquestionably measured in microseconds. For the same reason, humanity on the planet lags far behind. To ensure that this disparity is greatly decreased, numerous physicists and scientists are working hard to develop the most effective time-reducing method and lessen the time difference between the two planes.

As a result of light speed, physicists can identify time equations considerably more effectively and discover appropriate solutions to the corresponding difficulties.


Value of C helps in Detecting the Masses of the Objects

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Light has an extremely small mass, which allows it to travel at such a high speed. Other objects' masses can be increased or decreased by detecting or tracing this time-span and mass.

For the same reason, understanding the speed of light can assist humans in detecting the masses of numerous other things swiftly and efficiently.


Consistency in Objects Can be Traced Easily with the Value of C

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The speed of light is something that is constantly constant and is unaffected by any medium. This can be researched and applied to other items as well, and for the same reason, the value of the speed of light is undeniable in its place or manner.

To a large extent, all of the preceding statements describe the significance of the speed of light in the Physics discipline. For all of the aforementioned reasons, students should prioritize the speed of light to be totally relieved about Physics in the future.


Things to Remember

  • Value of c is a part of unit 2, chapter 3 Motion in a straight line in class 11 physics syllabus.
  • It carries a total of 11 to 14 periods and 3 to 5 marks. 
  • Speed of light plays an important role in understanding the dynamics of the moving objects.
  • It provides a very important connection between matter and energy through E = m*c²
  • Value of c sets the upper limit on the velocity of the signal between two objects.

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Sample Questions

Ques. Why should we symbolize the speed of light with 'c' only and not any other alphabet? (3 mark)

Ans. We symbolize the speed of light with ‘c’ because of the name of the speed of light in Latin, the right and most clear answer are. The speed of light is known as light celeritas in Latin, which means "the speed of light." Because a Latin Physicist introduces light, the speed of light is given the first alphabet as its sign. There is also a history of the use of the letter 'c' to represent the speed of light. Einstein first depicted the speed of light as a 'V.' However, his idea fell short of proving several features of the speed of light.

After several decades, a Latin physicist corrected all of Einstein's faults and symbolically denoted the speed of light as 'c' rather than 'V.' As a result, the symbol for the speed of light is 'c' because it is based on the same in Latin in the first place.

Ques. What factors are included in the formula of the speed of light? (3 mark)

Ans. In the first place, some well-known factors are involved in the formula for the speed of light. We all know that no factor in a formula arrives single-handedly, even if it is the c light constant or even if it is the centripetal force, and so on.

However, some equations may contain only two elements, and others may contain multiple factors.

The c speed of the light factor is related to the 'f' factor, which represents the frequency of light or that specific item.

As we all know, the speed of light is three times 10, which is 8 meters per second or 3 lakh kilometers per second. So, if students wish to calculate the speed of any other object, they should compare it to the speed of light and the frequency of the object in question. Without a doubt, the solution will be plainly discernible.

Ques. How can the value of C help in detecting the masses of the objects? (1 mark)

Ans. Light has an extremely small mass, which allows it to travel at such a high speed. Other objects' masses can be increased or decreased by detecting or tracing this time-span and mass.

Ques. What is the velocity of light in vacuum? (1 mark)

Ans. The speed of light is equal to 299792458 m/s ≅ 3×108 m/s.

Ques. What is the unit for the speed of light? (1 mark)

Ans. Light velocity can be described in terms of miles per hour (mph) or kilometers per second (km/s).

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CBSE CLASS XII Related Questions

  • 1.
    A 500 nm photon is incident normally on a perfectly reflecting surface and is reflected. The value of momentum transferred to the surface is:

      • \( 3.87 \times 10^{-43} \, \text{kg} \, \text{ms}^{-1} \)
      • \( 2.5 \times 10^{-30} \, \text{kg} \, \text{ms}^{-1} \)
      • \( 2.65 \times 10^{-27} \, \text{kg} \, \text{ms}^{-1} \)
      • \( 1.33 \times 10^{-27} \, \text{kg} \, \text{ms}^{-1} \)

    • 2.
      Determine the current in the \( 3 \, \Omega \) branch of a Wheatstone Bridge in the circuit shown in the figure.


        • 3.
          A circular coil of 100 turns and radius \( \left(\frac{10}{\sqrt{\pi}}\right) \, \text{cm}\) carrying current of \( 5.0 \, \text{A} \) is suspended vertically in a uniform horizontal magnetic field of \( 2.0 \, \text{T} \). The field makes an angle \( 30^\circ \) with the normal to the coil. Calculate:
          the magnetic dipole moment of the coil, and
          the magnitude of the counter torque that must be applied to prevent the coil from turning.


            • 4.
              Two small identical metallic balls having charges \( q \) and \( -2q \) are kept far at a separation \( r \). They are brought in contact and then separated at distance \( \frac{r}{2} \). Compared to the initial force \( F \), they will now:

                • attract with a force \( \frac{F}{2} \)
                • repel with a force \( \frac{F}{2} \)
                • repel with a force \( F \)
                • attract with a force \( F \)

              • 5.
                A ray of light MN is incident normally on the face corresponding with side AB of a prism with an isosceles right-angled triangular base ABC. Trace the path of the ray as it passes through the prism when the refractive index of the prism material is \( \sqrt{2} \), and \( \sqrt{3} \).


                  • 6.
                    The energy of an electron in an orbit in hydrogen atom is \( -3.4 \, \text{eV} \). Its angular momentum in the orbit will be:

                      • \( \dfrac{3h}{2\pi} \)
                      • \( \dfrac{2h}{\pi} \)
                      • \( \dfrac{h}{\pi} \)
                      • \( \dfrac{h}{2\pi} \)
                    CBSE CLASS XII Previous Year Papers

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