Electromagnetic Waves — Physics STD 12 Science — Question

In a TV tube, electrons are accelerated from the rear to the front. What is the direction of the current?

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?

What is called critical angle?

The radius of curvature of a concave mirror is 28 cm . Its focal length will be :

A carbon resistor is marked in colour bands of red, black, orange and silver. What is the resistance and tolerance value of the resistor?

What is the concept of direction of electric current ?

A resistance R is connected across a cell of emf ε and internal resistance r. A potentiometer now measures the potential difference between the terminals of the cell as V. Write the expression for 'r' in terms of ε, V and R.

Under what condition does a biconvex lens of glass having a certain refractive index act as a plane glass sheet when immersed in a liquid?