physics 1220 midterm 2

1.     Two resistors are connected in series across a potential difference. Resistor A has twice as much resistance as resistor B. If the current is carried by Resistor A is I. What is the current carried by B?

I

1.     A wire rod rolls with a speed of 20 m/s on two metallic rails 1.0m apart, that form a closed loop. If the magnetic field is 1.5T into the page, the power dissipated in the resistor R and the current direction are respectively

76mW clockwise by using I=2pirB/uo and the right hand rule curling your fingers around the rod

1.     The visible portion of the electromagnetic spectrum is closet to which of the following intervals

400 to 700nm

What is the direction of the magnetic field around a wire carrying a current perpendicular into this page?

it is clockwise around the wire in the plane of the page

   For a capacitor the

voltage lags behind the current

  Which of the following relations among the quantities in the figure is generally correct?

I3R3=I4R4 because they are parallel

  Light wave A has twice the frequency of light wave B. The wavelength of light wave A is --- light wave B.

half

   A positively charged particle moves with speed v in the positive x direction. A uniform magnetic field of magnitude B exists in the negative z direction. You want to balance the magnetic force with an electric field so that the particle will continue along a straight line. The electric field should be in the

negative y direction (+X,-Z)

   The switch S is initially at position b for a long time. It is then switched to position a, describe what happens to the light bulb as a function of time after the switch is flipped from b to a

the light bulb goes on but its brightness decreases with time and eventually goes off

The speed of ultraviolet radiation in free space compared with the speed of visible radiation in free space is

the same

  A uniform magnetic field is parallel to and in the direction of the positive z axis. For an electron to enter this field and not be deflected by the field, the electron must be travelling in which direction

along the z axis

   Tony charges a capacitor and then discharges it through a resistor. He notices that after two times constant, the voltage across the capacitor has decreased to –- of its value just prior to the initiation of the discharge

0.135 from the RC equation, e²

   uniform magnetic field produced by a large electromagnet. This field is changes at a steady rate from 0.650 T to 0.150T in 0.0100s. What is the magnitude of emf induced in the coil?

87V - BAcos=0.150-0.650= -0.50 Area=pi(5.25×10^-2)² = 8.65 × 10^-3 emf= (8.65×10^-3)(-0.50)/0.0100s x 200

  A copper ring lies in the yz plane as shown. The magnets long the x axis. Induced current flows through the ring as indicated. The magnet

must be flowing toward the ring

   After you measure the self-inductance of a coil, you unwind it and then rewind half the length of wire into a coil with the same diameter but half the number of turns. How does this change the self inductance?

it is quartered

   At what frequency is the reactance of 1.5Mh inductor equal to 5.0 ohms?

0.53 kHz because XL=2piFl F=5/(2pi)(1.5×10^-3)

The SI units of inductance times capacitance are

seconds squared

The wavelength of a 63.7 MHz electromagnetic wave is approximately

4.7m because y=f/c 3×10^8/6.37×10^6

In a circular loop of wire lying on a horizontal floor, the current is constant and, to a person looking downward has a clockwise direction. The accompanying magnetic field at the center of the circuit is directed

vertically downward

  Four identical light bulbs are connected to a power supply as shown. Which light consumes the most power?

bI