College Physics 2 - Test #2
Intensity
The energy a wave delivers to a unit area in a unit time
The voltage and current in a capacitor are not in phase.
The voltage lags by 90°.
In an RC circuit, the current across the resistor and the current across the capacitor are not in phase.
This means that the maximum current is not the sum of the maximum resistor current and the maximum capacitor current; they do not peak at the same time.
RL Circuits
When the switch is closed, the current immediately starts to increase. The back emf in the inductor is large, as the current is changing rapidly. As time goes on, the current increases more slowly, and the potential difference across the inductor decreases.
A changing magnetic field can induce
a current in a circuit.
When the switch is closed in this circuit,
a current is established that increases with time.
Visible light
a fairly narrow frequency range, from 4.3 x 1014 Hz (red) to 7.5 x 1014 Hz (violet).
Named portions of the spectrum, from the lowest frequencies to the highest
adio waves; microwaves; infrared; visible light; ultraviolet; X-rays; and gamma rays.
Polarized light has its electric fields
all in the same direction.
If the rod is to move at a constant speed,
an external force must be exerted on it. This force should have equal magnitude and opposite direction to the magnetic force.
Lenz's Law
an induced current always flows in a direction that opposes the change that caused
Phasor represents voltage or current in ac circuit;
as it rotates, its y component gives the instantaneous value.
Light scattered from the atmosphere is polarized when viewed
at right angles to the Sun
A transformer is used to
change voltage in an alternating current from one value to another.
Direction of current determines
charge
Faraday's experiment
close the switch in the primary circuit induces a current in the secondary circuit, but only while the current in the primary circuit is changing
Wall sockets provide
current and voltages that varies sinusoidally with time
Eddy current
current in a bulk conductor, can be powerful brakes
Accelerated charges radiate
electromagnetic waves
Any accelerated charge will emit
electromagnetic waves.
Current in the presence of a magnetic field will
feel a force
Infrared waves
felt as heat by humans. Remote controls operate using infrared radiation. The frequencies are from 1012 Hz to 4.3 x 1014 Hz.
X-rays
have higher frequencies still, from 1017 Hz to 1020 Hz. They are used for medical imaging.
An induced current flows
in a direction that opposes the change that caused it
Unpolarized light has its electric fields
in random directions.
If the magnetic field is increasing, the magnetic field created the induced current will be
in the opposite direction
Inductance occurs when a coil with a changing current
induces an emf in itself.
When light reflects from a horizontal surface,
it is partially polarized in the horizontal direction.
An electric motor is exactly the opposite of a generator
it uses the torque on a current loop to create mechanical energy.
If a charge capacitor is connected across an inductor
it will oscillate indefinitely without resistance
The polarization of a beam of light is the direction of
its electric field.
Smaller resistance
larger resonant current
An electric generator converts
mechanical energy into electric energy
No capacitance
more power and brighter
An electric motor is basically a generator
operated in reverse.
Electric and magnetic fields in an electromagnetic wave are
perpendicular to each other and to the direction of propagation, and are in phase.
A polarizer will transmit the component of light in the
polarization direction
Electromagnetic fields
produced by oscillating charges
Anytime an electric charge is accelerated it will
radiate
Ultraviolet light
starts with frequencies just above those of visible light, from 7.5 x 1014 Hz to 1017 Hz. These rays cause tanning, burning, and skin cancer. Some insects can see in the ultraviolet, and some flowers have special markings that are only visible under ultraviolet light.
The current in the secondary circuit is zero as long as
the current in the primary circuit and the magnetic field is not changing
The polarization of an electromagnetic wave refers to
the direction of its electric field.
The light exiting from a polarizer is polarized in
the direction of the polarizer.
Gamma rays
the highest frequencies of all, above 1020 Hz. These rays are extremely energetic, and are produced in nuclear reactions. They are destructive to living cells and are therefore used to destroy cancer cells and to sterilize food.
In a RLC circuit with an ac power source
the impedance is at a minimum at the resonant frequency
At high frequencies, the capacitive reactance is very small, while
the inductive reactance is very large.
Radio waves
the lowest-frequency electromagnetic waves that we find useful. Radio and television broadcasts are in the range of 106 Hz to 109 Hz.
The magnitude of the induced current is proportional to the rate at which
the magnetic field is changing
A conducting rod completes the circuit. As it falls,
the magnetic flux decreases and a current is induced
An emf is induce only when
the magnetic flux through a loop changes with time
Inductance
the proportionality constant that tells us how much emf will be induced for a given rate of change in current
The magnitude of the induced current depends on
the rate of change of the magnetic field.
the intensity of light is proportional to
the square of the field
If an unpolarized beam is passed through a polarizer,
the transmitted intensity is half the initial intensity.
The rms voltages across the capacitor and inductor must be the same;
therefore, we can calculate the resonant frequency.
t takes energy to establish a current in an inductor;
this energy is stored in the inductor's magnetic field.
Electromagnetic waves
traveling waves of oscillating electric and magnetic fields.
Forced due to the induced current is
upward, slowing the fall
Microwaves
used for cooking and also for telecommunications. Microwave frequencies are from 109 Hz to 1012 Hz, with wavelengths from 1 mm to 30 cm.
Magnetic flux is
used in the calculation of the induced emf
A beam of unpolarized light can be polarized by passing it through a polarizer,
which allows only a particular component of the electric field to pass through.
