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Chaps 7 & 8: Electricity and Magnetism Electricity:
A
negatively charged body has excess of electrons (gained electrons). Electrical conductors are materials in which electrons move freely. According to Coulomb's law the magnitude of the electric force between two charges is directly proportional to the product of the magnitude of the two charges. A hydrogen atom consists of a single proton and a single electron. If the distance between the proton and the electron were doubled, the electric force would be one fourth as much. What is the mathematical formula for the Coulomb's law? A device known as an electroscope can be used to determine the presence and kind of electric charge on an object. The laws of electrostatic charges states that like charges repel each other; unlike charges attract. A "Short" in an electric circuit means that current has found a lower resistance path and bypasses the desired circuit. In the same length of time, if different watts of appliances were compared, the most costly to operate would be the one with larger watts written on it. When a hard rubber rod is charged negatively by rubbing it with fur, the electrons are added to the rod. Two point charges 2 cm apart are moved to a new separation of 10 cm. By what factor does the mutual force between them change? The answer is 1/25; just use Coulomb's law to confirm it. A negatively charged rod is brought near one end of an uncharged metal bar, which is supported by an insulator. The end of the metal bar farthest from the charged rod (by induction) will be negative. The substance that contains the highest density of free electrons is iron. an electrical conductor has electric charges that move freely. Also an electrical insulator is best characterized by charges on the surface that don't move. A repelling force occurs between two charged objects that are of like signs, positive, positive or negative, negative. If body M with a positive charge is used to charge body N by induction, the charge left on body N must be negative. If body P with a positive charge is placed in contact with body Q, initially uncharged, the charge left on Q must be positive. When a glass rod is rubbed with silk, electrons are removed from the rod. Give me the units of electric field. If I use a positively charged rod to charge a ball by induction, the ball must be conductor. When charging two objects by rubbing them together, they must be made of different material. The chief characteristic of a superconducting wire is no resistance. Tripling the current in a circuit with constant resistance has the effect of changing the power by a factor of 9, how? If three resistors having values of 4.0, 6.0, and 8.0 are connected in series, then their total resistance is 18.0 ohms, what would be the total resistance when connected in parallel?
Magnetism: A magnet has two poles called as north and south poles. The discovery that a current-carrying wire deflects a compass needle was made by Oersted during his class lecture at the university of
Copenhagen. The angle between magnetic north and geographic north on the earth's surface is called angle of declination. Geophysicists generally attribute the existence of the earth's magnetic field to convection
currents within the liquid interior. Magnetic declination refers to the angle between directions to true north and magnetic north. One difference between electrical charges and magnetic poles is that a magnetic pole
cannot be isolated. The electrical protection of fuses and circuit breakers depends on opening the circuit in cases of overload and shorting. A smaller unit of ampere is milliamp, which is one millionth of an ampere. A
magnetic field is produced by electric charges in motion. A north magnetic pole and a south magnetic pole always occur together. Also do problems, which were done in the class and during the lectures. Some numerical
questions will come from there. Light and Other Electromagnetic Waves: The law of reflection says that the angle of incidence equals the angle of reflection. When a ray of light enters into denser medium it
bends towards normal and also its speed reduces somewhat. Can you define focal length of a lens? The plane polarized light vibrates in one plane only. The color of light depends on its wavelength. What is the wavelength
of the red light? A book appears blue in sunlight because only blue light is reflected and all other colors are absorbed. Light travels from sun to the earth, 93 million miles away, in 500 seconds, which is quite a
large time. An electromagnetic wave is made up of electric and magnetic fields. In order to catch overspeeding, the police radar uses the principle of Doppler effect. How does red light differ from green light? Answer
is given earlier. Maxwell made the theoretical prediction that electromagnetic waves travel through a vacuum at the speed of light. It was Hertz who first built and operated devices that could emit and detect
man-made electromagnetic radiation. In order to keep food hot, restaurants have to place it under infrared lamp. When charge particles accelerate they emit electromagnetic radiation. The human eye is sensitive to light
with a wavelength as low as 390mm, which corresponds to frequency of 7.7x1014 Hz. When listening to a singer on an AM radio station, the basic frequency of the radio wave neither depend on the frequency of
the note being sung by the singer nor on the speed of the radio waves. If the velocity of light through a liquid is measured at 2.4x108 m/s, then the index of refraction is 1.33. A ray of white light incident upon a
glass prism is dispersed into various colors. Which color experiences the greatest angle of deviation? When red light and green light are mixed yellow color appears. Polarized sunglasses help when skiing on snow on a
sunny day because reflection polarizes the light from the snow. The eye doctor to correct farsightedness will prescribe a converging lens. Explain myopia and hyperopia! A Spectrum of colors seen on an oil slick
on a wet street is primarily a result of interference and the light with wavelength greater than 6000 A0
appears to have the general color of red. A prism separates white light into colors called dispersion of light and white light seen on a screen when green light is mixed with magenta. Why a red rose appears to be red in the white light?
HomeWork Problems The current in a 60 watt, 120 volt lamp is
a. 1/2 amp c. 90 amps
b. 2 amps d. 7200 amps
Two point charges separated by 1.5 cm have charge values of +2.0 x10 6 and 4.0 x10 6. What is the mutual force between them? (k=9x10 9 N m 2 /C2 )
a. 320 N c. 8x10 12 N
b. 3.6x10 8 N d. 3.1x10 3 N A metallic object holds a charge of 3.8x10 6
C. what total number of electrons does this represent? (e=1.6x10 19 C) a. 4.2x10 14
c. 2.4x10 13 b. 6.1x10 13
d. 1.6x10 14
If a 75 W light bulb operates at a voltage of 120 V, the current in the bulb is
a. 0.63 A c. 9.0x10 3 A
b. 1.6 A d. 1.1x10 4 A
Tripling the current in a circuit with constant resistance has the effect of changing the power by a factor of
a. 0.33 c. 3.0
b. 1/9 d. 9.0
If a 500 W heater carries a current of 4.0 A, the voltage across the ends of the heating element is
a. 2000 V c. 250 V
b. 125 V d. 0.008 V
The heating coil of a hot water heater has a resistance of 20 ohms and operates at 210 V. Its power rating is
a. 8.8x10 5 W c. 10.5 W
b. 2205 W d. 2940 W
Compared to the velocity of light, the velocity of radio waves is a. less c. the same
b. greater d. infinite
Microwave ovens emit a frequency intended to be in resonance with which of the following? a. frequency of water molecules b. size of oven compartment c. frequency of metal lining of oven
d. frequency of food molecules Police radar uses the principle of a. interference c. Doppler effect
b. resonance d. refraction Red light differs from green light in
a. amplitude c. wavelength
b. velocity d. intensity A negatively charged body has
a. lost electrons c. lost protons b. gained electrons d. gained protons
Electrical conductors are materials a. that have an excess of electrons b. that have a deficiency of electrons c. that repel electrons d. in which electrons move freely
The magnitude of the electric force between two charges is a. inversely proportional to the distance between them b. directly proportional to the product of the magnitudes of the two charges
c. proportional to the charge on only one of them d. proportional to the distance between them cubed A hydrogen atom consists of a single proton and a single electron. If the distance between the proton and the
electron were doubled, the electric force would be a. 1/4 as much c. twice as much
b. 1/2 as much d. four times as much The formula F = k q1 q2/d2
a. Joule's law c. Ohm's Law b. Coulomb's law d. Faraday's
A device that is used to determine the presence and kind of electric charge on an object is a. an electrostatic precipitator b. a dynamo c. a voltaic pile d. an electroscope
The statement that like charges repel each other while unlike charges attract is the basis of the a. electron theory of matter b. law of electric charges c. conservation of charge d. law of electrostatic force
A magnet a. has two poles b. can be made of any metal c. must be wrapped with wire d. exhibits static electricity The discovery that a current-carrying wire deflects a compass needle was made by
a. Franklin c. Henry b. Faraday d. Oersted
The angle between magnetic north and geographic north on the earth's surface is called a. terrella c. angle of declination
b. angle of dip d. action-at-a-distance An electrical conductor has a. low mass density b. high tensile strength c. electric charges that move freely d. poor heat conductivity
Geophysicists generally attribute the existence of the earth's magnetic field to a. convection currents within the liquid interior b. iron ore deposits in the crust c. nickel-iron deposits in the crust
d. solar flares Magnetic declination refers to the a. angle between the earth's magnetic field and earth's surface b. earth's magnetic field strength at the equator
c. tendency for the earth's field to reverse itself d. angle between directions to true north and magnetic north One difference between electrical charges and magnetic poles is that a. opposite magnetic poles repel
b. one magnetic pole cannot create magnetic poles in other materials c. a magnetic pole cannot be isolated d. magnetic poles do not produce magnetic fields One millionth of an ampere is a
a. milliamp c. kiloamp b. microamp d. nanoamp A magnetic field is produced a. only by a permanent magnet
b. by electric charges in motion c. by electric charges at rest d. by electric charges both at rest and in motion A north magnetic pole and a south magnetic pole a. always occur together b. repel each other
c. can be separated and isolated d. occur at the earth's north and south geographic poles The first person to reconize the connection between electricity and magnetism was....
a. Benjamin Franklin b. Charles Coulomb c. Hans Christian Orsted d. Michael Faraday The north arrow of compass points to a....
a. south magnetic pole deep in the Earth. b. north magnetic pole deep in the Earth. c. none of the above. d. both a and b An object that acquires an excess of electrons becomes a (an)
a. ion b. negatively charged object c. positively charged object A quantity of electric charge is measured in a unit called a (an)
a. Coulomb b. volt c. amp d. watt In an electric current the electrons are moving
a. at a very slow rate b. at the speed of light c. faster than speed of light d. unknown
If you multiply amps x volts, the answer will be in units of
a. resistance b. work c. current d. power
The unit of resistance is the a. watt b. ohm c. amp d. volt The Earth's north magnetic pole
a. is located at the geographic North pole b. is a magnetic south pole c. both are correct d. is magnetic north
A current-carrying wire has a magnetic around it because a. a moving charge produces a magnetic field of its own b. the current aligns the magnetic filed of its own
c. the metal was magnetic before the current before the current was established d. none of the above is correct According to the electromagnetic wave model, visible light is produced when
a. an electric charge is accelerated with a magnitude within a given range b. an electric charge is moved with a constant speed
c. a blackbody is heated above zero d. an object absorbs electromagnetic radiation
Before it travels through the earth's atmosphere, sunlight is mostly a. infrared radiation b. visible light c. ultraviolet radiation d. blue light
You are able to see in shaded areas, such as under a tree, because light has undergone a. refraction b. incident bendingc. a change in speed d. diffuse reflection An image that is not
produced by light rays coming from the image, but is the result of your brain's interpretations of light rays is called a(n)
a. real image b. imagined image c. virtual image d. phony image
The ration of speed of light in a vacuum to the speed of light in some transparent materials is called
a. the critical angle b. total internal reflection c. the law of reflection d. the index of refraction The polarization behavior of light is best explained by considering light to be
a. longitudinal waves b. transverse waves c. particles d. particles with ends, or poles
The sky appears to be blue when the sun is high in the sky because a. blue is the color of air, water, and other fluids in large amount b.red light is scattered more than blue
c. blue light is scattered more than other colors d. none of the above |
