Moving Charges and Magnetism

Topics in this chapter

• Magnetic Fields From Currents
• Magnetic Forces and Charged Motion
• Forces, Torque, and Magnetic Dipoles
• Galvanometers and Magnetic Measurements

Cheat sheet

Practice questions

1. Question 1Q-E44E5A

   A proton and an alpha particle are projected perpendicular to a uniform magnetic field with the same kinetic energy. The ratio of the radii of their circular paths ($r_p : r_\alpha$) is:

   1. A.1 : 1
   2. B.1 : \sqrt{2}
   3. C.\sqrt{2} : 1
   4. D.2 : 1
   See the answer and solution
2. Question 2Q-53B5D1

   A circular coil of radius $R$ and $N$ turns carries a current $I$. The magnetic field at its center is $B$. At what distance from the center along the axis of the coil will the magnetic field be $B/8$?

   1. A.$\sqrt{3}R$
   2. B.$\sqrt{2}R$
   3. C.$2R$
   4. D.$3R$
   See the answer and solution
3. Question 3Q-173A54

   A galvanometer of resistance $G$ is converted into a voltmeter to measure up to $V$ volts by connecting a resistance $R_1$ in series. If it is to be converted to measure up to $2V$ volts, the series resistance required is $R_2$. The relation between $R_1$ and $R_2$ is:

   1. A.$R_2 = 2R_1 + G$
   2. B.$R_2 = 2R_1 - G$
   3. C.$R_2 = R_1 + G$
   4. D.$R_2 = 2R_1$
   See the answer and solution
4. Question 4Q-95DBA0

   A long straight wire carries a current $I$. The magnetic field at a perpendicular distance $r$ from the wire is $B$. If the current is doubled and the distance is halved, the new magnetic field becomes:

   1. A.$B / 4$
   2. B.$B / 2$
   3. C.$2B$
   4. D.$4B$
   See the answer and solution
5. Question 5Q-ED1BE1

   A rectangular loop of sides $10\text{ cm}$ and $5\text{ cm}$ carrying a current $2\text{ A}$ is placed in a uniform magnetic field of magnitude $0.3\text{ T}$. The maximum torque acting on the loop is:

   1. A.$3 \times 10^{-3}\text{ N m}$
   2. B.$6 \times 10^{-3}\text{ N m}$
   3. C.$3 \times 10^{-2}\text{ N m}$
   4. D.$1.5 \times 10^{-2}\text{ N m}$
   See the answer and solution