1. Why is the safety feature of a garage door opener mounted about 10 inches off...

1. Why is the safety feature of a garage door opener mounted about 10 inches off the floor rather than higher?

2.Why do photons have to be massless?

Expert Solution

1) All openers must include a second safety reversing feature such as photoelectric eyes. These are installed near the floor. Once the invisible beam is broken, the door reverses automatically.

The photo eyes mentioned above should not be installed higher than six inches above the garage floor. If the eyes are installed higher, a person or pet could get under the beam and not be detected by the photo eyes.

2) According to the special theory of relativity, any particle with a finite mass requires an infinite amount of energy to reach the speed of light. Therefore no particles with any intrinsic mass can travel with the speed of light.

The energy required to attain a speed v is given by

E = mc^2(( 1/√1-v^2/c^2) - 1).

As v approaches c, E approaches infinity.

Only massless particles are allowed to travel at the speed of light. Photon is massless, hence it can travel with the speed of light. The energy of a photon is given by E=pc where p is the momentum of the photon.

genius_generous answered 2 years ago

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