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ISC Class 12 Physics Solved Question Paper 2005

Short Answer Type

41.

Why are neutrons considered as ideal particles for nuclear fission reactions ? Calculate the energy released in the following nuclear reaction.

₁H²+ ₁H²→₂H⁴ +energy

(mass of 1H² = 2.014102 u, mass of ₂He⁴ = 4.002604 u).

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42. What is LED ? Explain how radiations are given out by LED.

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43. The output of a OR gate is connected to a NOT gate as shown in the figure given below. Name the new gate formed. Draw the logic symbol and truth table of the new gate.

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Long Answer Type

44. Two cells of same e.m.f. E, but different internal resistance r₁ and r₂ are connected to an external resistance R as shown in the figure. The voltmeter V reads zero. Obtain an expression for R in terms of r₁ and r₂. Calculate the voltage across the cell of internal resistance r₂. (Assume that the voltmeter V is of infinite resistance).

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45. In the figure given below, PQ is a long straight wire carrying a current of 5A in the direction of the arrow. An electron travels with a velocity of 10⁶ m/s at a distance 10 cm from the wire in the same direction of the current. Calculate the magnitude and direction of the force experienced by the electron.

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46. Explain with necessary formula (no derivation) how you will compare the magnetic moments of two magnets by equal distance method using a deflection magnetometer in tan A position.

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47.
(i) With proper labelling of the axis, draw the input and output characteristic curves of a npn transistor in common emitter configuration.

(ii) Define current gain for a transistor in common emitter configuration.

i) Input characteristics of npn transistor in CE mode.

A graph between input voltage (V_BE) and input current (I_B) keeping collector voltage (V_CE) constant is called input characteristics.

There is no current when V_BE is less than the barrier voltage. When V_BE exceeds the barrier voltage, I_B increases and reaches maximum.

Output characteristics :

A graph between collector voltage (V_CE) and collector current (I_c) keeping input current (I_B) constant is called output characteristics.

As V_CE is increased I_c increases first and then it remains almost constant and is independent of V_CE.

(ii) Current gain of transistor in CE mode :

It the ratio of change in collector current to the change in base current when collector-emitter voltage is kept constant.