Atoms — Physics STD 12 Science — Question

A circular loop of radius 20cm carries a current of 10A. An electron crosses the plane of the loop with a speed of 2.0 × 10⁶m/s. The direction of motion makes an angle of 30° with the axis of the circle and passes through its centre. Find the magnitude of the magnetic force on the electron at the instant it crosses the plane.

A uniform conducting wire of length 12a and resistance R is wound up as a current carrying coil in the shape of:

1. An equilateral triangle of side a.
2. A square of sides a.
3. A regular hexagon of sides a. The coil is connected to a voltage source V₀. Find the magnetic moment of the coils in each case.

Draw a labelled ray diagram of a refracting telescope. Define its magnifying power and write the expression for it.
Write two important limitations of a refracting telescope over a reflecting type telescope.

Find the magnetic field B due to a semicircular wire of radius 10.0cm carrying a current of 5.0A at its centre of curvature.

radioactive isotope has a half-life of 5 years. After how much time is its activity reduced to 3.125% of its original activity?

A certain sample of a radioactive material decays at the rate of 500 per second at a certain time. The count rate falls to 200 per second after 50 minutes.

1. What is the decay constant of the sample?
2. What is its half-life?

A ball falls on the ground from a height of 2.0m and rebounds up to a height of 1.5m. Find the coefficient of restitution.

1. Identify the part of the electromagnetic spectrum which is:

1. Suitable for radar system used in aircraft navigation,
2. Produced by bombarding a metal target by high-speed electrons.

2. Why does a galvanometer show a momentary deflection at the time of charging or discharging a capacitor? Write the necessary expression to explain this observation.