ch 25 physics
A step-up transformer steps up voltage by ten times. If voltage input is 120 volts, voltage output is
1200 10 x 120=1200
Disconnect a small-voltage battery from a coil of many loops of wire and a large voltage may be produced by
the sudden collapse in the magnetic field
A transformer transforms voltage while
transferring energy from one coil to another
In the field induction credited to Maxwell, wires
wires are not needed
Neon signs require about 12,000 volts to operate. If the circuit uses a 120-volt power source, the ratio of primary to secondary turns on the transformer should be
1 primary to 100 secondary
A certain transformer doubles input voltage. If the primary coil draws 10 A of current, then the current in the secondary coil is
5 A if the transformer doubles than the secondary coil is half of the 1st coil
The metal detectors that people walk through at airports operate via
Faraday's law
Underlying the concept of self-induction is
Faraday's law
The discovery of electromagnetic induction is credited to
Joseph Henry in America. Michael Faraday in England
When voltage is stepped up in a transformer, current is stepped down. But Ohm's law tells us that greater voltage means greater current, not less current. How then can current be lower when voltage is increased?
Ohm's law applies to the circuit connected to the secondary, not to the transformer. Current in the secondary is lower when compared to the greater current drawn by the primary
The primary of a transformer connected to 200 V has 100 turns. The secondary has 10 turns. This is a step-down transformer
Vout= Nprimary/ Vin (N secondary) 20V= 160turns/200V(10turns)
Faraday's law underlies the operation of
a shake flashlight. an electric guitar. the changing of traffic lights
When a change occurs in the magnetic field in a closed loop of wire
a voltage is induced in the wire. electromagnetic induction occurs. a current is created in the loop of wire
The current produced by a common generator is
ac
The principal advantage of ac power over dc power is that
ac voltage can be transformed via conventional transformers
A friend says that changing electric and magnetic fields underlie the production of light
agree with friend
When voltage is induced in a coil of wire, current is
also induced
Rapid change of a magnetic field induces
an electric field
An electric motor is very similar to
an electric generator
A generator armature is more difficult to rotate when supplying electric current due to
an induced magnetic field in the windings that resists change
The high voltage that is important in a power line is high voltage
between the parallel wires of a line
Voltage can be induced in a wire by
changing the current in a nearby wire. moving the wire near a magnet. moving a magnet near the wire.
A step-up transformer steps up voltage by ten times. Neglecting slight losses, if 100 W of power go into the primary coil, the power coming from the secondary coil is
coils get same power 100w
The principle difference between a step-up and step-down transformer is
different ratios of turns of wire for each.
Thrust a magnet into the opening of a rubber band and it
do nothing
Induced electric and magnetic fields result in
electromagnetic waves
The output power of an ideal transformer is
equal to the input power
A device that transforms mechanical energy into electrical energy is a
generator
An iron core in a transformer
guides magnetic field lines
If you thrust a magnet into a closed loop of wire, the loop will
have a current
If you drop a bar magnet in a vertical copper pipe it will fall slowly because
it induces a magnetic field in the pipe that resists motion of the magnet
Power is transmitted at high voltages because the corresponding current in the wires is
low so that overheating of the wires is minimized
Electromagnetic induction occurs in a coil when there is a change in
magnetic field intensity in the coil
Electromagnetic induction is employed in
mobile phones. hybrid automobiles. electric power lines. triggering traffic lights
A device that transforms electrical energy to mechanical energy is a
motor
An efficient step-down transformer decreases
not power and not energy neither of these
A turbogenerator produces
not power and not energy, but transforms energy from one form to another/ transforms them does not creat them
High-voltage wires in power lines are not high-current wires because the current in them is
not the same as the current that powers the distant load. proportional to the voltage drop from beginning to end of each line, rather low
If the primary of a transformer is connected to a dc power source, the transformer would have a voltage output
only while being connected or disconnected dc stands for connected and disconnected
The induced electric and magnetic fields of Maxwell are
perpendicular to each other
The rate at which energy is transferred is
power
When a bar magnet is thrust into a coil of copper wire, the coil tends to
repel the magnet as it enters
Magnetic field strength inside a current-carrying coil will be greater if the coil encloses a
rod of iron
Between the consumer and the power plant, most importantly, are
step down transformers
The primary of a transformer is the coil connected to
the input power line
The secondary of a transformer is the coil connected to
the load
Compared to the primary voltage, the secondary voltage can be
the same, lower or higher any of these
Disregarding the effects of friction, a cyclist will coast farther when a lamp powered by a wheel generator is
turned off.
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
twice
A transformer actually transforms
voltage
An efficient step-up transformer boosts
voltage
