Ch. 9 homework
An ideal transformer has 50 turns in the primary and 500 turns in the secondary. An input of 12 V will produce an output of
120 V
The voltage across the input terminals of a transformer is 110 V. The primary coil has 50 loops and the secondary coil has 100 loops. The output is
220 V
An electronic game requires 6 V for operation. With a transformer it can be powered by a 120-V outlet. If the primary has 500 turns, the secondary has
25 turns
An electronic game requires 6 V for operation. With a transformer it can be powered by a 120-V outlet. If the primary has 500 turns, the secondary has
440 W
A transformer has an input of 6 V and an output of 42 V. If the input is changed to 12 V, the output would be
84 V
What are the basic differences and similarities between a generator and an electric motor?
A generator converts mechanical energy to electrical energy; a motor converts electrical energy into mechanical energy.
Why is iron magnetic and wood not magnetic?
Atoms in wood are not so strongly magnetic that they organize into domains as iron atoms do
The metal detectors that travelers walk through at airports operate via
Faraday's Law
When a bar magnet is thrust into a coil of wire, a greater voltage is induced with
a greater number of loops in the coil and a stronger bar magnet. and faster thrusting motion.
Surrounding every moving electron is
a magnetic and electric field
A compass needle in a magnetic field experiences
a torque
A galvanometer calibrated to read potential difference is
a voltemeter
A friend says that changing electric and magnetic fields underlie the production of light.
agree with your friend
A galvanometer calibrated to read current is
an ammeter
Like kinds of magnetic poles repel while unlike kinds of magnetic poles
attract
When a current-carrying wire is bent into a loop, its magnetic field inside the loop
becomes concentrated
Compared with the current in the primary coil of a transformer, the current in the secondary coil
can be greater or less
The magnetic field lines about a straight current-carrying wire are
circular
Electromagnetic induction is employed in
computers, mobile phones, and credit card readers
A common electromagnet consists of a
current-carrying coil with a piece of iron inside.
The principal difference between a step-up and step-down transformer is
different ratios of turns for each set of loops or coils.
When an electron passes through the magnetic field of a horseshoe magnet, the electron's
direction of motion is changed
Moving electric charges are surrounded by
electric and magnetic fields
Surrounding every stationary electron is
electric field
The fact that a force is exerted on a current-carrying wire when in a magnetic field is employed in
electric meters and motors
Faraday's law describes
electromagnetic induction
What any type of field generation cannot create is
energy
Power is the rate at which
energy is transferred
Compared with the huge force that attracts an iron tack to a strong magnet, the force that the tack exerts on the magnet is
equally huge
An iron nail is attracted
equally to either pole of a magnet
Magnet A has twice the magnetic field strength of magnet B and pulls on magnet B with a force of 100 N. The amount of force that magnet A exerts on magnet B is
exactly 100 N
A device that transforms mechanical energy to electrical energy is a
generator
If you break a bar magnet in half you'll
have two magnets
Magnetic domains normally occur in
iron
The magnetic field strength inside a current-carrying coil will be greater if the coil encloses a
iron rod
Compared with a motor, a generator is
its opposite
Electric and magnetic fields combine to produce
light
Wood does not have magnetic properties because it contains no
magnetic domains
The ultimate source of all magnetism is
moving electric charge
Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a
north pole
The minimum or no magnetic force on a moving electron occurs for motion
parallel to the magnetic field.
The induced electric and magnetic fields of Maxwell are
perpendicular to each other
Maximum magnetic force occurs when electrons move
perpendicular to the magnetic field direction.
A strong magnetic field easily penetrates
plastic coatings and human flesh
The rate at which a transformer transfers energy is called
power
Since magnetic force on a moving electron is always perpendicular to its direction of motion, magnetic force is unable to change an electron's
speed
Magnetism is due to the motion of electrons as they
spin on their axes. and move around the nucleus.
A topic that most underlies electrical studies and all of physics is
the conservation of energy
Voltage produced by a generator alternates because
the magnetic field that produces it alternates.
The magnetic field inside a current-carrying coil increases when
the number of loops of wire in the coil increases and an iron core is inserted and current is increased.
Compared with the power input to an ideal transformer, the power output is
the same
When a bar magnet is broken in half, the strength of the four new poles relative to pole strength before breaking is
the same
When a bar magnet is thrust at the same speed into a coil having twice the number of loops, the induced voltage is
twice as much
Every magnet contains at least
two poles
A step-up transformer in an electrical circuit can step up
voltage
An efficient step-down transformer decreases
voltage
The frequency with which a magnet plunges into and out of a wire coil equals the frequency of the induced
voltage and current
The energy source for a generator may be
wind and steam from a turbine and a waterfall.
A magnetic field exists in a current-carrying coil of wire
with or without a contained piece of iron.
