1. A wire is carrying a current $I$ is placed in a region of uniform magnetic field B1​. The magnitude of the magnetic field is $B$, and its direction is into the page. The force acting on the wire is $F$, as shown in the diagram.

The wire, carrying the same current $I$, is now placed with the orientation shown into another region of uniform magnetic field B2​. The magnitude of the magnetic field is $B$, and its direction is out of the page.

What is the correct direction and magnitude of the force acting on the wire in field B2​?

	Direction	Magnitude
A.		$F$
B.		$F$
C.		$F\sin \theta$
D.		$F\sin \theta$

2. Planet $A$ has a gravitational field strength $g$ at its surface. Planet $B$ has twice the density and twice the radius of planet $A$.

What is the gravitational field strength at the surface of $B$?

3. Two positive charges of magnitude $2C$ and $8C$ respectively are placed 9cm apart. A third charge is introduced between the two charges as shown below;

At what separation, X, from the 2C charge is the electric field strength equal to zero?

4. Two sections of current-carrying wires, $X$ and $Y$, that lie in the plane of the paper, are shown below. The arrow in wire $X$ shows the direction of conventional current. Which response gives possible directions of current in wire $Y$ and electromagnetic force acting on $Y$?

5. Satellites $A$ and $B$ orbit the same planet of mass $M$. Satellite $A$ has a mass of $3m$ and it is located at a height of $R$ from the surface of the planet. Satellite $B$ has a mass of $m$ and it is located at a height of 2$R$ from the surface of the planet.

What is the ratio of the centripetal force acting on $A$ to the centripetal force acting on $B$?

6. A hydrogen nucleus is held stationary in a uniform vertical electric field, represented by the arrows. Which of the paths shown would require the largest work to be done on the hydrogen nucleus?

7. Four fixed charged point particles are at the vertices of a rectangle. Which arrow represents the net electric field at the center of the rectangle?

8. An astronaut in a space station orbiting the earth experiences weightlessness.

The following are three statements about the astronaut and the space station:

• I.  The astronaut experiences no gravitational force.
• II.  The centripetal acceleration of the space station is equivalent to the gravitational field strength at that location
• III.  Both the astronaut and the space station have the same acceleration.

Which of these statements is correct?

9. In the following diagram, the size of the charges is small compared to the distance R.

What is the direction of the force on the charge in the center?

10. The centers of three masses lie on the same line. The centers of the masses are separated as shown.

The net gravitational force on m2​ is zero when the value of $d$ is one third of $x$. What is the ratio m1/m3​​?

11. A satellite of mass $m$ is in an orbit at a height $h$ from the surface of a planet of mass $M$. The centripetal force acting on the satellite is $F$ and the linear speed is $v$.

What is the new centripetal force and linear orbital speed when it is moved to a new orbit at $2h$ from the surface of the planet?

12. A proton and another object with charge +e exert electrical and gravitational forces on one another. To the nearest order of magnitude, what mass must the object have to be so that the net force acting on it is zero?

13. An object of mass $m$ and charge $q$ is dropped vertically between two parallel plates, $K$ and $L$. A magnetic field $B$ can be created perpendicular to the plane of the paper. The electric field between plates is $E$.

Which of the following is correct about the magnitude of magnetic and electric fields when the object falls vertically at a constant velocity v?

14. A source of radiation is near a magnetic field that is directed into the page. A sheet of paper is placed in the path of the radiation before it enters the magnetic field.

The gamma radiation is not deflected when entering the magnetic field. Which of the following is correct about the other type of radiation that penetrates the paper sheet and the direction of its deflected path in the magnetic field?

15. Two point charges are separated by a distance $r$ as shown.

16. Two charges separated by a distance $r$ are placed in a medium with permittivity $ϵ$. The charges are then moved to air so that they have the same force between them as that in the medium.

17. Two positive charges q1​ and q2​ are separated by a distance $d$. A third positive charge $q$ is placed at a distance d/4 from q1​ so that the charge $q$ is in equilibrium.

What is the ratio q1/q2​​?

18. A conductor carrying electric current out of the plane of the paper is placed between two magnets as shown in the diagram.

At which location is the magnitude of the resultant magnetic field strength largest due to the conductor and the magnets?

19. The gravitational field strength on the surface of the moon is gE/6​​. Two objects of different masses $m$ and $2m$ are released with zero speed on the moon from heights of $h$ and $2h$, respectively, where $h$ is small compared to the radius of the moon.

What are the magnitudes of the accelerations of these objects right after release?

20. A plastic rod carrying a uniformly distributed positive charge is bent into a quarter-circle. What is the direction of the electric field at point $P$?

21. Two charges, separated by a large distance, are shown below, along with the electric field lines around each charge.

Which of the following statements is correct?

• I.  The charge $q$ is positive.
• II.  The charge $q$ is equal in magnitude to $+Q$.
• III.  The electric field magnitude near the charge $q$ is greater than the magnitude of the field near the charge $+Q$.

22. A current-carrying wire is at right angles to a uniform magnetic field. The magnetic force per unit length on the wire is F/L. The length of the wire, the magnitude of the magnetic field strength, and the current of the wire are all doubled. Which of the following is the magnetic force per unit length on the wire after these changes?

23. Which of the following correctly lists the fundamental forces in decreasing order of strength?

24. A positive and a negative charge of equal magnitude are located on the same horizontal line.

What is the direction of the net electric field at the point marked X, equidistant from the two charges?

25. The diagram below shows a circuit connected to an iron rod $XY$. The connecting wires are flexible. The rod is placed in a magnetic field directed perpendicularly into the page as shown.

In what direction will the resultant force act on the rod when the current is switched on in the circuit?