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more than the resistance of either lamp
When two lamps are connected in series to a
battery, the electrical resistance that the battery
“senses” is
less than the resistance of either lamp
Chapter 20: DC Circuits | Electric Circuits
When two lamps are connected in parallel to a
battery, the electrical resistance that the battery
“senses” is
series
On some early automobiles both headlights failed
when one bulb burned out. The headlights were
likely connected in
exactly 100 N
Magnet A has twice the magnetic field strength of
Magnet B and at a certain distance pulls on magnet
B with a force of 100 N. The amount of force that
magnet A exerts on magnet B is
equally huge
Compared to the huge force that attracts an iron tack
to a strong magnet, the force that the tack exerts on
the magnet is
attract
Like kinds of magnetic poles repel while unlike
kinds of magnetic poles
CANNOT (Nothing in classical electrodynamic theory or quantum
mechanics says that magnetic monopoles can’t exist)
Whereas electric charges can be isolated, magnetic
poles
An electric field
Surrounding every stationary electron is
a magnetic and electric field (This magnetic field is a result of “distortions” in the
electric field caused by the motion of the electron.)
Surrounding every moving electron is
Circular
The shape of a magnetic field surrounding a current-
carrying conductor is
at right angles to the direction of the motion.
The direction of the force exerted on a moving
charge in a magnetic field is
a voltage is induced in the wire
a current is created in the loop of wire.
electromagnetic induction occurs.
When a change occurs in the magnetic field in a
closed loop of wire
twice
When a magnet is moved to and fro in a wire coil,
voltage is induced. If the coil has twice as many
loops, the voltage induced is
how frequently a magnet dips in and out of the
coil.
The frequency of induced voltage in a wire coil
depends on
wide and thick
Will water flow more easily through a wide pipe or a narrow pipe? Will current flow more easily through a thick wire or a thin wire?
increases
Does heating a metal wire increase or decrease its electrical resistance
ohm
What is the unit of electrical resistance?
Current is reduced to HALF
If the voltage impressed across a circuit is held constant while the resistance doubles, what change occurs in the current?
The current will DECREASE to half its previous value
If the resistance of a circuit remains constant while the voltage across the circuit decreases to half its former value, what change occurs in the current?
Wetness decreases resistance
How does wetness affect the resistance of your body?
It grounds the case to zero potential, by connecting the appliance body directly to ground. (PREVENTS YOU FROM GETTING ELECTRIC SHOCK)
What is the function of the round third prong in a modern household electrical plug?
Battery= DC
Generator= AC
Does a battery produce dc or ac? Does the generator at a power station produce dc or ac?
the direction of the current flow changes 60 times per second.
What does it mean to say that a certain current is 60 Hz?
It is a one-way valve that allows electrons to in one direction only
. What property of a diode enables it to convert ac to pulsed dc?
A capacitator
A diode converts ac to pulsed dc. What electrical device smoothes the pulsed dc to a smoother dc?
also 1 A (both circuits are in series)
In a circuit of two lamps in series, if the current through one lamp is 1 A, what is the current through the other lamp?
4 (subtract)
. If a voltage of 6 V is impressed across the circuit in the preceding question and the voltage across the first lamp is 2 V, what is the voltage across the second lamp?
6 V
. In a circuit of two lamps in parallel, if there is a voltage of 6 V across one lamp, what is the voltage across the other lamp?
The sum of the currents in the branches equals the current through the source.
How does the sum of the currents through the branches of a simple parallel circuit compare with the current in the voltage source
to prevent overloading the circuit with current
What is the function of fuses or circuit breakers in a circuit?
Hans Christian Oersted
By whom, and in what setting, was the relationship between electricity and magnetism discovered
Their motion
The force between electrically charged particles depends on the magnitude of each charge, their separation distance, and what else?
the movement of electrical charges
What is the source of magnetic force?
Like poles repel, unlike poles attract, and the force is proportional to the inverse square of the distance between two poles.
Is the rule for the interaction between magnetic poles similar to the rule for the interaction between electrically charged particles?
All magnets have both south and north poles. Electric charges can exist as singular entities.
In what way are magnetic poles very different from electric charges?
The field strength is stronger where the field lines are closer.
. How does magnetic field strength relate to the closeness of magnetic field lines about a bar magnet?
Electric charges in motion
What produces a magnetic field?
Revolution and spin
What two kinds of rotational motion do electrons in an atom appear to have?
The magnetic field is directed along concentric circles surrounding the wire
What is the direction of the magnetic field surrounding a current-carrying wire
The magnetic field reverses direction at every point. A clockwise pattern of concentric circles becomes a counterclockwise pattern of concentric circles and vice versa.
What happens to the direction of the magnetic field about an electric current when the direction of the current is reversed?
The magnetic field of each segment of wire in the loop, due to electrons moving in the wire, adds together inside the loop, thereby making the field become bunched-up.
Why is the magnetic field strength greater inside a current carrying loop of wire than about a straight section of wire?
true
True or false: A charged particle must move in a stationary magnetic field in order that a force due to the field act on it
perpendicular/parallel
In what direction relative to a magnetic field does a charged particle move in order to experience maximum deflecting force? Minimum deflecting force?
reduces intensity
What effect does Earth’s magnetic field have on the intensity of cosmic rays striking Earth’s surface?
perpendicular
What relative direction between a magnetic field and a current-carrying wire results in the greatest force?
An electric current flows through a wire in a magnetic field. The deflection force on the wire acts against a spring. The compression of the spring is proportional to current.
How does a galvanometer detect electric current?
ammeter/voltmeter
What is a galvanometer called when it has been calibrated to read current? When it has been calibrated to read voltage?
current is reversed once per half-turn (180°) of the rotor.
How often is current reversed in the loops of an electric motor?
YES
Is it correct to say that an electric motor extends the physics that underlies a galvanometer?
The core is too hot to allow atoms to maintain a constant magnetic orientation.
Why are there probably no permanently aligned magnetic domains in Earth’s core
where Earth's magnetic field switches direction, causing the north and south magnetic poles to swap places
What are magnetic pole reversals?
caused by the interaction between the Earth's magnetic field and charged particles from the solar wind.
. What is the cause of the aurora borealis (northern lights)?
the phenomenon of electromagnetic induction
What important discovery did physicists Michael Faraday and Joseph Henry make?
The magnetic field through the coil must change.
What must change in order for electromagnetic induction to occur in a wire coil?
a changing magnetic field induces an electric field
(The induced voltage in a coil is proportional to the number of loops, to the area of the loops, and to the rate of change of the magnetic field through the loops)
State Faraday’s law
Move a magnet near the loop, move the loop near a magnet, change current in a nearby loop
What are the three ways in which voltage can be induced in a loop of wire
self-induction
When the magnetic field changes in a coil of wire, voltage in each loop of the coil is induced. Will voltage be induced in a loop if the source of the magnetic field is the coil itself?
