Phy 214 Test 3 10 points each 0pts Absolutely free! Spring 2007

1. Give the direction of the force on the charged particle when it enters the region where the magnetic field is located in each case below. To indicate out of the page, use a circle with a dot in its center, to indicate into the page, use a circle with a x in its center. Indicate any other direction with an arrow in that direction.

1'. What direction of current in the wire produces the magnetic field shown.

1''. An electron moving along the positive x axis perpendicular to a magnetic field experiences a magnetic deflection in the negative y direction. What is the direction of the magnetic field?

2. A proton moving at 4 x 10⁶ m/s through a magnetic field of 2 T experiences a magnetic force of magnitude

8 x10^-13 N. What is the angle between the proton's velocity and the field?

2'. A proton moves perpendicular to a uniform magnetic field B at 1.00 _ 107 m/s and experiences an acceleration of 2.00 _ 1013 m/s2 in the +x direction when its velocity is in the +z direction. Determine the magnitude and direction of the field.

2''. A proton moves with a velocity of v = (2i – 4j + k ) m/s in a region in which the magnetic field is B = (i + 2j – 3k ) T. What is the magnitude of the magnetic force this charge experiences?

3. Review Problem. A rod of mass 0.720 kg and radius 6.00 cm rests on two parallel rails (see Fig. below) that are d = 12.0 cm apart and L = 45.0 cm long. The rod carries a current of I = 48.0 A (in the direction shown) and rolls along the rails without slipping. A uniform magnetic field of magnitude 0.240 T is directed perpendicular to the rod and the rails. If it starts from rest, what is the speed of the rod as it leaves the rails?

3'. A wire 2.80 m in length carries a current of 5.00 A in a region where a uniform magnetic field has a magnitude of 0.390 T. Calculate the magnitude of the magnetic force on the wire assuming the angle between the magnetic field and the current is (a) 60.0°, (b) 90.0°, (c) 120°.

3''. A conductor suspended by two flexible wires as shown in Figure P29.14 has a mass per unit length of 0.040 0 kg/m. What current must exist in the conductor in order for the tension in the supporting wires to be zero when the magnetic field is 3.60 T into the page? What is the required direction for the current?

4. In Figure below, the current in the long, straight wire is I1 = 5.00 A and the wire lies in the plane of the rectangular loop, which carries the current I2 = 10.0 A. The dimensions are c = 0.100 m, a = 0.150 m, and _ = 0.450 m. Find the magnitude and direction of the net force exerted on the loop by the magnetic field created by the wire.

4'. A wire with a mass of 1.00 g/cm is placed on a horizontal surface with a coefficient of friction of 0.200. The wire carries a current of 1.50 A eastward and moves horizontally to the north. What are the magnitude and the direction of the smallest vertical magnetic field that enables the wire to move in this fashion?

5. What current is required in the windings of a long solenoid that has 1 000 turns uniformly distributed over a length of 0.400 m, to produce at the center of the solenoid a magnetic field of magnitude 1.00 x 10^-4 T?

6pg. The flexible loop in Figure P20.10 has a radius of 12 cm and is in a magnetic field of strength 0.15 T. The loop is grasped at points A and B and stretched until its area is nearly zero. If it takes 0.20 s to close the loop, find the magnitude of the average induced emf in it during this time.

6pg '. A 500-turn circular-loop coil 15.0 cm in diameter is initially aligned so that its axis is parallel to the Earth’s magnetic field. In 2.77 ms, the coil is flipped so that its axis is perpendicular to the Earth’s magnetic field. If an average voltage of 0.166 V is thereby induced in the coil, what is the value of the Earth’s magnetic field at that location?

6. Consider the current-carrying loop shown in Figure below, formed of radial lines and segments of circles whose centers are at point P. Find the magnitude and direction of B at P.

6'. A conductor consists of a circular loop of radius R and two straight, long sections, as shown in Figure P30.6. The wire lies in the plane of the paper and carries a current I. Find an expression for the vector magnetic field at the center of the loop.

6''. The segment of wire in Figure P30.7 carries a current of I = 5.00 A, where the radius of the circular arc is R = 3.00 cm. Determine the magnitude and direction of the magnetic field at the origin.

6'''. (a) A conductor in the shape of a square loop of edge length _ = 0.400 m carries a current I = 10.0 A as in Fig. P30.3. Calculate the magnitude and direction of the magnetic field at the center of the square.

6''''. Two parallel conductors carry currents in opposite directions, as shown in the figure below. One conductor carries a current of 10.0 A. Point A is the midpoint between the wires, and point C is 5.00 cm to the right of the 10.0-A current. I is adjusted so that the magnetic field at C is zero. Find (a) the value of the current I and (b) the value of the magnetic field at A.

8. In Figure P31.30, the bar magnet is moved toward the loop. Is Va - Vb positive, negative, or zero? Explain.

8'. Use Lenz's law to answer the following questions concerning the direction of induced currents. (a) What is the direction of the induced current in resistor R in Figure P31.28a when the bar magnet is moved to the left? (b) What is the direction of the current induced in the resistor R immediately after the switch S in Figure P31.28b is closed? (c) What is the direction of the induced current in R when the current I in Figure P31.28c decreases rapidly to zero? (d) A copper bar is moved to the right while its axis is maintained in a direction perpendicular to a magnetic field, as shown in Figure P31.28d. If the top of the bar becomes positive relative to the bottom, what is the direction of the magnetic field?

7. A Boeing 747 jet with a wingspan of 60.0 m is flying horizontally at a speed of 300 m/s over Phoenix, Arizona, at a location where the Earth’s magnetic field is 50.0 _T at 58.0° below the horizontal. What voltage is generated between the wingtips?

7'.

Assume R = 6 ohms , l = 1/2 m and the uniform 2.5 T magnetic field is directed into the page. At what speed must the bar be moved to produce a current of .5 A in the resistor?

7''. Same fig as 7'. A conducting rod of length _ moves on two horizontal, frictionless rails, as shown in Figure P31.20. If a constant force of 1.00 N moves the bar at 2.00 m/s through a magnetic field B that is directed into the page, (a) what is the current through the 8.00-_ resistor R?

9. a. Find the direction of the current in the resistor R when the magnet is dropped from above just after it has passed through the ring.

b. Find the direction of the current in the resistor R just after the switch is opened.

10. Calculate the resistance in an RL circuit in which L = 2.50 H and the current increases to 90.0% of its final value in 3.00 s.

10'. A 12.0-V battery is connected into a series circuit containing a 10.0-Ω resistor and a 2.00-H inductor. How long will it take the current to reach 50.0% of it's maximum value?

10''. In the circuit shown in Figure below, let L = 7.00 H, R = 9.00 _, and _ = 120 V. What is the self-induced emf 0.200 s after the switch is closed?

10'''. A 12.0-V battery is connected in series with a resistor and an inductor. The circuit has a time constant of 500 x10^-6s, and the maximum current is 200 mA. What is the value of the inductance?