What is the refraction index of the material of a plano-convex lens, if the radius of curvature of the convex surface is \(10~\text{cm}\) and the focal length of the lens is \(30~\text{cm}?\)

1. \(1/3\)

2. \(1\)

3. \(4/3\)

4. \(2/3\)

Subtopic: Lens Makers' Formula |

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Q32:

A parallel plate capacitor of capacitance C is connected to a battery and is charged to a potential difference V.
Another capacitor of capacitance 2C is connected to another battery and is charged to potential difference 2V. The charging batteries are now disconnected and the capacitors are connected in parallel to each other in such a way that the positive terminal of one is connected to the negative terminal of one is connected to the negative terminal of the other. The final energy of the configuration is

1. Zero

2.

3.

4.

Subtopic: Energy stored in Capacitor |

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Q33:

The n rows each containing m cells in series are joined in parallel. Maximum current is taken from this combination across an external resistance of 3 Ω. If the total number of cells used is 24 and internal resistance of each cell is 0.5 Ω, then

1. m = 8, n = 3

2. m = 6, n = 4

3. m = 12, n = 2

4. m = 2, n = 12

Subtopic: Grouping of Cells |

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Q34:

If the intensities of the two interfering beams in Young’s double-slit experiment are

and

then the contrast between the maximum and minimum intensities are good when

1.

Subtopic: Young's Double Slit Experiment |

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Q35:

A simple telescope, consisting of an objective of focal length 60 cm and a single eye lens of focal length 5 cm is focused on a distant object in such a way that parallel rays emerge from the eye lens. If the object makes an angle of 2 º at the objective, then the angular width of the image is

1. 10 º

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Q36:

A semiconductor has an electron concentration of \(8\times10^{13}\text{ per cm}^3\) and a hole concentration of \(5\times10^{12}\text{ per cm}^3.\) The electron mobility is \(25000\text{ cm}^2\text{V}^{-1}\text{s}^{-1}\) and the hole mobility is \(100\text{ cm}^2\text{V}^{-1}\text{s}^{-1}\) Then,
1. the semiconductor is \(n\)-type
2. the conductivity is \(320\text{ m-mho-cm}^{-1}\)
3. Both \((1)\) and \((2)\)
4.None of the above

Subtopic: Types of Semiconductors |

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Q37:

An ammeter and a voltmeter are joined in series to a cell. Their readings are A and V respectively. A resistance is now joined in parallel with the voltmeter. Then,

1. Both A and V will increase

2. Both A and V will decrease

3. A will decrease, V will increase

4. A will increase, V will decrease

Subtopic: Grouping of Cells |

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Q38:

Three identical capacitors A, B and C are charged to the same potential and then made to discharge through three resistance . Their potential differences (V) are plotted against time t, giving the curves 1, 2 and 3. Choose the incorrect option.

1.

2.

3.

4. None of the above.

Subtopic: Capacitance |

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Q39:

The diffraction pattern of a single slit consists of a central bright band which is:

1.	wide, and is flanked by alternate dark and bright bands of decreasing intensity
2.	narrow, and is flanked by alternate dark and bright bands of equal intensity
3.	wide, and is flanked by alternate dark and bright bands of equal intensity
4.	narrow and is flanked by alternate dark and bright bands of decreasing intensity