The Flow of Electrons as Electric Current

Q. Current in conductors is due to flow of positive charges.

1. True
2. False

Q. An electron is moving in a circular path of radius $5.1\times {10}^{-11}$ m at a frequency of $6.8\times {10}^{15}$ revolutions/sec. The equivalent current is approximately equal to _______.

1. $5.1\times {10}^{-3}A$
2. $6.8\times {10}^{-3}A$
3. $1.1\times {10}^{-3}A$
4. $2.2\times {10}^{-3}A$

Q. The distance between charges $5\times {10}^{-11}$C and $-2.7\times {10}^{-11}$C is $0.2m$. The distance at which a third charge should be placed in order that it will not experience any force along the line joining the two charges is

1. 0.44 m
2. 0.65 m
3. 0.556 m
4. 0.350 m

Q. The currect through a wire depends on time as,
$i=(10+4t)$
Here, $i$ is in ampere and $t$ in seconds. Find the charge crossed through a section in time interval between $t=0$ to $t=10\text{s}$.

1. $300\text{C}$
2. $400\text{C}$
3. $500\text{C}$
4. $600\text{C}$

Q. Pranav once had put his finger inside the electrical socket and had gotten a bad electric shock. When he learned about random motion of electrons and then the drift speed when there is a current, he concluded that drift speed must be very high compared to the speed of random motion and that is why you get electric shocks when there is a current. Is he right?

1. The drift speed of electrons is usually very high compared to the order of speed of random motion due to temperature.
2. The drift speed is comparable to the order of speed of random motion due to temperature.
3. The drift speed is slightly lesser (maybe a few times lesser) than the order of speed of random motion due to temperature.
4. The drift speed is very very less compared to the order of speed of random motion due to temperature.

Q. The belt of an electrostatic generator is $50cm$ wide and travels $30cm/s$. The belt carries charge into the sphere at a rate corresponding to ${10}^{-4}A$. What is the surface density of charge on the belt?

1. $6.7\times {10}^{-5}C{m}^{-2}$
2. $6.7\times {10}^{-7}C{m}^{-2}$
3. $6.7\times {10}^{-4}C{m}^{-2}$
4. $6.7\times {10}^{-8}C{m}^{-2}$

Q. In a hydrogen discharge tube it is observed that through a given cross-section $3.13\times {10}^{15}$electrons are moving from right to left and $3.12\times {10}^{15}$protons are moving from left to right. What is the electric current in the discharge tube and what is its direction

1. 1mA towards right
2. 1mA towards left
3. 2mA towards left
4. 2mA towards right

Q. A point charge q is moving towards conducting spherical shell at constant velocity v. Shell is connected to ground.

1. As charge moves towards shell, current flows from shell to earth.
2. As charge approaches shell, current increases.
3. Current increases linearly.
4. Current decreases as charge approaches shell.

Q. In the Bohr’s model of hydrogen atom, the electrons moves around the nucleus in a circular orbit of a radius $5\times {10}^{-11}$ metre. It’s time period is $1.5\times {10}^{-16}$ sec. The current associated is

1. Zero
2. $1.6\times {10}^{-19}A$
3. $0.17A$
4. $1.07\times {10}^{-3}A$

Q. The current through a wire depends on time as $I=(2+3t)\text{A}$. Calculate the charge crossed through a cross-section of the wire in $10\text{s}$.

1. $17\text{C}$
2. $170\text{C}$
3. $150\text{C}$
4. $20\text{C}$

Q. In an electrolyte $3.2\times {10}^{18}$ bivalent positive ions drift to the right per second while $3.6\times {10}^{18}$ monovalent negative ions drift to the left per second. Then the current is

1. 1.6 amp to the left
2. 1.6 amp to the right
3. 0.45 amp to the right
4. 0.45 amp to the left