Exam 2 Chapters 23-28 Flashcards
An electron moves at right angles to a magnetic field of 0.18T. What is its speed if the force exerted on it is 8.9E-15 N?
Find the radius of an electrons orbit when it moves perpendicular to a magnetic field of 0.66t with a speed of 6.27E5 m/s.
mv^2/r = qvb
Charged particles pass through a velocity selector with electric and magnetic fields at right angles to each other, as shown in the figure. If the electricfield has a magnitudeof 450 N/C and the magnitude field has a magnitude of 0.18T, what speed must the particles have to pass through the selector undeflected?
What is the magnetic force exerted on a 2.15m length of wire carrying a current of 0.899A perpendicular to a magnetic field of 0.720T?
The maximum current in a superconducting solenoid can be as large as 3,750A. If the number of turns per meter in such a solenoid is 3,650, what is the magnitude of the magnetic field it produces?
Two parallel wires, each carrying a current of 2.2A in the same direction, are shown in the figure. Find the direction and magnitude of the net magnetic field at points A, B, and C.
A rectangular loop of wire 0.24m by 0.36m is bent into an L shape as shown in the figure. The magnetic field in the vicinity of the loop has a magnitude of 0.035T and points in a direction 25 degrees below the Y-axis. The magnetic field has no x component. Find the magnitude of the magnetic flux through the loop.
phi= BA cos(theta)
phi= (0.035T)(0.24x0.36)(cos25+cos65 degrees)
phi= 4 meters
A single conducting loop of wire has an area of 7.2E-2m^2 and a resistance of 110 ohms. Perpendicular to the plane of the loop is a magnetic field of strength 0.48T. At what rate (in T/s) must this field change if the induced current in the loop is to be 0.32A?
How do the resistance, capacitive reactance, and inductive reactance change when the frequency in a circuit is increased?
In an a.c. circuit, an inductor produces inductive reactance which causes the current to lag the voltage by 90 degrees. Because the inductor “reacts” to a changing current, it is known as a reactivecomponent. The opposition that an inductor presents to a.c. is called inductive reactance (XL). This opposition is caused by the inductor “reacting” to the changing current of the a.c. source. Both the inductance and the frequency determine the magnitude of this reactance. This relationship is stated by the formula:
A 3.33-kOhm resistor is connected to a generator with a maximum voltage of 141V. Find (a) the average and b. the maximum power delivered to this circuit.
The reactance of a capacitor is 65ohms at a frequency of 57Hz. What is its capacitance?
Find the impedance of a 60Hz circuit with a 45 Ohm resistor connected in series with a 95 uF capacitor.
Predict/Explain When a long copper wire of finite resistance is connected to an ac generator, as shown in figure (a), a certain amount of current flows through the wire. The wire is now wound into a coil of many loops and reconnected to the generator, as indicated in Figure. (a) Is the current supplied,to the coil greater than, less than, or the same as the supplied to the uncoiled wire? (b) Choose the best explanation from among the following.
I. More current flows in the circuit because the coiled wire is an inductor and inductors tend to keep the current flowing in an ac circuit
II. The current supplied to the circuit is the same because the wire is the same. Simply wrapping the wire in a coil changes nothing.
III. Less current is supplied to the circuit because the coiled wire acts as an inductor, which increases the impedance of the circuit.
III. Less current is supplied to the circuit because the coiled wire acts as an inductor, which increases the impedance of the circuit.
An inductor, also called a coil, choke or reactor, is a passive two-terminal electrical component which resists changes in electric current passing through it.
Find the frequency at which a 33 uF capacitor has the same reactance as a 33mH inductor. What is the the resonance frequency of an LC circuit made with this inductor and capacitor?
Two RLC circuits have different values of L and C. Is it possible for these two circuits to have the same resonance frequency? Explain.
The resonant frequency of RLC circuit is 1/2piSqrt(L*C)
If the product L*C is same for the two circuits in question then you can have the same resonant frequency for eg the circit with 6H inductance and 1F capacitance will have same resonant frequency as 3H inductance and 2F capacitance
An electric charge on the r axis oscillates sinusoidally about the origin. A distant observer is located at a point on the *y axis.
(a) In what direction will the electric field oscillate at the observer’s location?
(b) In what direction will the magnetic field oscillate at the observer’s location?
(c) In what direction will the electromagnetic wave propagate at the observer’s location?
Y= Electromagnetic wave
X= Electric field
Z= Magnetic field (oscillates in the plane perpendicular to the electric field and is also perpendicular to the direction of propagation)
- (a) The electric field will oscillate in the x direction
- (b) The magnetic field will oscillate in the z direction.
- (c) The electromagnetic wave will propagate in the positive y direction.
Most of the galaxies in the universe are observed to be moving away from Earth. Suppose a particular galaxy emits orange light with a frequency of 5.000 x 10E14 H2. If the galaxy is receding from Earth with a speed oI 3325 km/s, what is the frequency of the light when it reaches Earth?
NEED TO REWRITE ANSWER! Consider a spiral galaxy that is moving directly away from Earth with a speed V : 3.600 x 105 m/s at its center as shown in Figure 15-26. The galaxy is also rotating about its center, so that points in its spiral arms are moving with a speed of : 6.400 x 105 m/s relative to the center. If light with a frequency of 8.230 x 10^14 H2 is emitted in both arms of the galaxy, what frequency is detected by astronomers observing the arm that is moving (a) toward and (b) away from Earth (Measurements of this type are used to map out the speed of various regions in distant, rotating galaxies.)
Dental X-rays: X-rays produced in the dentist’s office typically have a wavelength of 0.30 nm. What is the frequency of these rays?
Communicating with a Submarine Normal radiofrequency waves cannot penetrate more than a few meters below the surface of the ocean. One method of communicating with submerged submarines uses very low frequenry (VLF) radio waves. What is the wavelength (in air) of a 10.0-kHz VLF radio wave?
The Hale Telescope: The 200-inch-diameter concave mirror of the Hale telescope on Mount Palomar has a focal length of 16.9 m. An astronomer stands 20.0 m in front of this mirror.
(a) Where is her image located? Is it in front of or behind the mirror?
(b) Is her image real or virtual? How do you know?
(c) What is the magnification of her image?
The image is real because its behind the lens
Find the ratio of the speed of light in water to the speed of light in a diamond.
Light enters a container of benzene at an angle of 43 degrees to the normal; the refracted beam makes an angle of 27 degrees with the normal. Calculate the index of refraction of benzene.
(a) Use a ray diagram to determine the approximate location of the image produced by a concave lens when the object is at a distance 1/2 f the lens.
(b) Is the image upright or inverted?
(c) Is the image real or virtual? Explain.
An object is a distance f /2 from a convex lens.
(a) Use a ray diagram to find the approximate location of the image.
(b) Is the lmage upright or inverted? (c) Is the image real or virtual? Explain.
Two lenses that are 35 cm apart are used to form an image, as shown in the figure. Lens 1 is diverging and has a focal length of f1= -7.0 cm; lens 2 is converging and has a focal length f2= 14 cm. The object is placed 24 cm to the left of lens 1.
(a) Use a ray diagram to find the approximate location of the image.
(b) Is the image upright or inverted?
(c) Is the image real or virtual? Explain.
An object is a distance 2f fron a convex lens.
(a) Use a ray diagram to find the approximate location of the image.
(b) Is the image upright or inverted?
(c) Is the image real or virtual? Exphin.
Two lenses that are 35 cm apart used to form an image as shown in the figure. Lens 1 is converging and has a focal length f1= 14cm. Lens 2 is diverging and has a focal length f2- -7cm. The object is placed 24 cm to the left of lens 1.
a. ) Use a ray diagram to find approximate location of the image
b. ) is the image upright or inverted?
c. ) Is the image real or virtual? Explain.
- The image is located just to theleft of lens 2
- The image is inverted
- Since the final image is on the same side of Lens 2 as its object (the original image, which is real), it is VIRTUAL
In Young’s two-slit experiment, the first dark fringe above the central bright fringe occurs at an angle of 0.31 degrees. What is the ratio of the slit separatiory d, to the wavelength of the light?
Light from a He-Ne laser ( wavelength= 632.8 nm) strikes a pair of slits at normal incidence, forming a double-slit interference pattern on a screen located 1.4m from the slits shows the interference pattern observed on the screen. What is the slit separation?
A magnetic field is oriented at an angle of 47 degrees to the normal of a rectangular area 0.051m by 0.068m. If the magnitude flux through this surface has a magnitude of 4.8E-5 Txm^2 what is the strength of the magnetic field?
MRI Soleniod: The magnetic field produced by an MRI solenoid 2.5m long and 1.2m in diameter is 1.7T. Find the magnitude of the magnetic flux through the core of a solenoid.
A solenoid with 385 turns per meter and a diameter of 0.17m has a magnetic flux through its core of magnitude 1.28E-4 Txm^2. Find the current in this solenoid. How would your answer to part a change in the diameter of the solenoid were doubled? Explain.
A single conducting loop of wire has an area of 7.2E-2m^2 and a resistance of 110 ohms. Perpendicular to the plane of the loop is a magnetic field of strength 0.48T. At what reate (in T/s) must this field change if the induced current in the loop is to be 0.32A?
Consider the circuit shown in the figure 23-39. Assuming the inductor in this circuit has the value l= 6.1mH, how much energy is stored in the inductor after the switch has been closed a long time?
This figure shows the magnitude flux through a single loop coil as a function of time. What is the induced emf in the coil at t= 0.05s, t= 0.15s, and t=0.50s?
I= (N)BA = (N)BAcos(Ø) (Usually we don’t use N)
Where N= Number of turns on the wire
At t= 0.05sec
£= -Change in Epsilon/ Change in time > £= (10Wb-0Wb) / (0.1s-0s) £= -100V
*Change value to volts
ON QUIZ: A long straight wire carries a current I, as indicated in the fure. Three small metal rings are placed near the current carrying wire (A and C) or directly on top of it. If the current in the wire is increasing with time, indicate whether the induced emf in each of the rings is clockwise, counterclockwise or zero. Explain your answer for each ring.
Use Right Hand Rule:
Thumb- Force
Pointer Finger- Current
Middle Finger- Magnetic Field
Ring B: Epsilon= BAcos(0) + BAcos(180) = 1 + -1 = 0
Consider the RLC circuit shown in the figure. When the switch is closed, the current in the circuit is observed to increase from 0 to 0.32A in 0.15s. What is the inductance L? How long after the switch is closed does the current have the value 0.50A? What is the maximum current that flows in this circuit?
A rectangular loop of wire 0.24m by 72m is bent into an L shape as shown in the figure. The magnetic field in the vicinity of the loop has a magnitude of 0.035T and points in a direction 25 degrees below the Y-axis. The magnetic field has no x component. Find the magnitude of the magnetic flux through the loop.
