Current Electricity — Physics STD 12 Science — Question

For transistor action, which of the following statements are correct:

1. Base, emitter and collector regions should have similar size and doping concentrations.
2. The base region must be very thin and lightly doped.
3. The emitter junction is forward biased and collector junction is reverse biased.
4. Both the emitter junction as well as the collector junction are forward biased.

The thermal energy developed in a current-carrying resistor is given by U = i² Rt and also by U = Vit. Should we say that U is proportional to i² or i?

The speed of light is 299,792,458m/s.

1. With respect to the earth.
2. With respect to the sun.
3. With respect to a train moving on the earth.
4. With respect to a spaceship going in outer space.

A steel wire of cross-sectional area 0.5mm² is held between two fixed supports. If the wire is just taut at 20^°C, determine the tension when the temperature falls to 0^°C. Coefficient of linear expansion of steel is 1.2 × 10^-5 °C^-1 and its Young's modulus is 2.0 × 10¹¹N m^-2.

Write expression in vector form for produced magnetic field due to small part of a current carrying conductor in Biot-Savart law.

On a metallic target, when high energy electrons are struck, electromagnetic waves are produced. Name these waves.

Define intensity of magnetisation.

When a body is weighed on an ordinary balance we demand that the arm should be horizontal if the weights on the two pans are equal. Suppose equal weights are put on the two pans, the arm is kept at an angle with the horizontal and released. Is the torque of the two weights about the middle point (point of support) zero? Is the total torque zero? If so, why does the arm rotate and finally become horizontal?