Question
Through what potential difference should an electron be accelerated to give it a speed of: 
  1. 0.6c
  2. 0.9c
  3. 0.99c

Answer

  1. $\text{eV}-\text{m}_0\text{C}^2=\frac{\text{m}_0\text{C}^2}{2\sqrt{1-\frac{\text{V}^2}{\text{C}^2}}}$

$\Rightarrow\text{eV}-9.1\times10^{-31}\times9\times10^{16}$

$=-\frac{9.1\times9\times10^{-31}\times10^{16}}{2\sqrt{1-\frac{0.36\text{C}^2}{\text{C}^2}}}$

$\Rightarrow\text{eV}-9.1\times9\times10^{-15}$

$=\frac{9.1\times9\times10^{-15}}{2\times0.08}$

$\Rightarrow\text{ev}-9.1\times9\times10^{-15}$

$=\frac{9.1\times9\times10^{-15}}{1.6}$

$\Rightarrow\text{eV}=\Big(\frac{9.1\times9}{1.6}+9.1\times9\Big)\times10^{-15}$

$=\text{eV}\Big(\frac{81.9}{1.6}+81.9\Big)\times10^{-15}$

$=\text{eV}=133.0875\times10^{-15}$

$\Rightarrow\text{V}=83.179\times10^{4}=831\text{KV}$

  1. $\text{eV}=\text{m}_0\text{C}^2=\frac{\text{m}_0\text{C}^2}{2\sqrt{1-\frac{\text{V}^2}{\text{C}^2}}}$

$\Rightarrow\text{eV}-9.1\times9\times10^{-19}\times9\times10^{16}$

$=\frac{9.1\times9\times10^{-15}}{2\sqrt{1-\frac{0.81\text{C}^2}{\text{C}^2}}}$

$\Rightarrow\text{eV}-81.9\times10^{-15}=\frac{9.1\times9\times10^{-15}}{2\times0.435}$

$\Rightarrow\text{eV}=12.237\times10^{-15}$

$\Rightarrow\text{V}=\frac{12.237\times10^{-15}}{1.6\times10^{-19}}=76.48\text{kV}$

$\text{V}=0.99\text{C}=\text{ev}-\text{m}_0\text{C}^2=\frac{\text{m}_0\text{C}^2}{2\sqrt{1-\frac{\text{V}^2}{\text{C}^2}}}$

$\Rightarrow\text{eV}=\frac{\text{m}_0\text{C}^2}{2\sqrt{1-\frac{\text{V}^2}{\text{C}^2}}}+\text{m}_0\text{C}^2$

$=\frac{9.1\times10^{31}\times9\times10^{16}}{2\sqrt{1-(0.99)^2}} +9.1\times10^{-31}\times9\times10^{16}$

$\Rightarrow\text{eV}=372.18\times10^{-15}$

$\Rightarrow\text{V}=\frac{372.18\times20^{-15}}{1.6\times10^{-19}}=272.6\times10^{4}$

$\Rightarrow\text{V}=2.726\times10^{6}=2.7\text{MeV}$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Similar questions

Find the maximum magnifying power of a compound Microscope having a 25 diopter lens as the objective, a 5 diopter lens as the eyepiece and the separation 30cm between the two lenses. The least distance for clear vision is 25cm.
The friction coefficient between the board and the floor shown in figure is $\mu.$ Find the maximum force that the man can exert on the rope so that the board does not slip on the floor.

Consider a situation similar to that of the previous problem except that the ends of the rod slide on a pair of thick metallic rails laid parallel to the wire. At one end the rails are connected by resistor of resistance R.
  1. What force is needed to keep the rod sliding at a constant speed v?
  2. In this situation what is the current in the resistance R?
  3. Find the rate of heat developed in the resistor.
  4. Find the power delivered by external agent exerting the force on the rod.
A solid wire of radius 10cm carries a current 5.0A distributed uniformly over its cross-section. Find the magnetic field B at a point at a distance (a) 2cm (b) 10cm and (c) 20cm away from the axis. Sketch a graph of B versus x for 0 < x < 20cm.
An aluminium can of cylindrical shape contains 500cmof water. The area of the inner cross section of the can is 125cm2. All measurements refer to 10°C. Find the rise in the water level if the temperature increases to 80°C. The coefficient of linear expansion of aluminium = 23 × 10-6 °C-1 and the average coefficient of volume expansion of water = 3.2 × 10-4 °C-1 respectively.
i. Describe, with the help of a suitable diagram, the working principle of a step-up transformer. Obtain the relation between input and output voltages in terms of the number of turns of primary and secondary windings and the currents in the input and output circuits.
i. Given the input current 15 A and the input voltage of 100 V for a step-up transformer having 90% efficiency, find the output power and the voltage in the secondary if the output current is 3 A.
A boy riding on a bicycle going at 12km/h towards a vertical wall whistles at his dog on the ground. If the frequency of the whistle is 1600Hz and the speed of sound in air is 330m/s, find
  1. The frequency of the whistle as received by the wall.
  2. The frequency of the reflected whistle as received by the boy.
Two tiny spheres carrying charges 1.5 µC and 2.5 µC are located 30 cm apart. Find the potential and electric field:
  1. At the mid-point of the line joining the two charges, and
  2. At a point 10 cm from this midpoint in a plane normal to the line and passing through the mid-point.
  1. Using Biot-Savart’s law, derive the expression for the magnetic field in the vector form at a point on the axis of a circular current loop.
  2. What does a toroid consist of ? Find out the expression for the magnetic field inside a toroid for N turns of the coil having the average radius r and carrying a current I. Show that the magnetic field in the open space inside and exterior to the toroid is zero.
Consider a non-conducting plate of radius r and mass m that has a charge q distributed uniformly over it. The plate is rotated about its axis with an angular speed $\omega.$ Show that the magnetic moment $\mu$ and the angular momentum of the plate are related as $\mu=\frac{\text{q}}{2\text{m}}\text{l}.$