Optical fibre is based on:
1. Total internal reflection
2. Less scattering
3. Refraction
4. Less absorption coefficient

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The speed of light in media \(M_1\) and \(M_2\) is \(1.5\times10^{8}\) m/s and \(2.0\times10^{8}\) m/s respectively. A ray of light enters from medium \(M_1\) and \(M_2\) at an incidence angle \(i.\) If the ray suffers total internal reflection, the value of \(i\) is:
| 1. | equal to or less than \(\text{sin}^{-1}\left (\frac{3}{5} \right )\) |
| 2. | equal to or greater than \(\text{sin}^{-1}\left (\frac{3}{4} \right )\) |
| 3. | less than \(\text{sin}^{-1}\left (\frac{2}{3} \right )\) |
| 4. | equal to \(\text{sin}^{-1}\left (\frac{2}{3} \right )\) |

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| 1. | \(\sin^{-1 }(1/2)\) | 2. | \(\sin^{-1 }( 1/5)\) |
| 3. | \(\sin^{-1 }(4/5)\) | 4. | \(\sin^{-1 } (3/4)\) |
Total internal reflection can take place only if:
| 1. | the light goes from optically rarer medium (smaller refractive index) to optically denser medium. |
| 2. | the light goes from optically denser medium to rarer medium. |
| 3. | the refractive indices of the two media are close to each other. |
| 4. | the refractive indices of the two media are widely different. |

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| 1. | \(v(1-\cos \theta)\) | 2. | \(\dfrac{v}{\sin \theta}\) |
| 3. | \(\dfrac{v}{\cos \theta}\) | 4. | \(v \cos \theta\) |