Physics test 3
When the resistors are connected in 2 loops (first circuit of the video) the current through the resistors are 1 mA and 10mA. What is the current in the circuit before the junction that splits to the 2 resistors?
11 mA
Four unequal resistors are connected in a parallel with each other. Which one of the following statements is correct about this combination?
The equivalent resistance is less than that of the smallest resistor.
Four unequal resistors are connected in series with each other. Which one of the following statements is correct about this combination?
The equivalent resistance is more than the largest resistance.
Which one of the following statements is correct? A) Earth's geographic north pole is the north pole of Earth's magnetic field. B) Earth's geographic south pole is the south pole of Earth's magnetic field. C) The north pole of a magnet points towards Earth's geographic north pole. D) The north pole of a magnet points towards Earth's geographic south pole. E) None of the above statements is correct.
The north pole of a magnet points towards Earth's geographic north pole.
The electromagnetic spectrum consists of
Radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays and gamma rays
Which of these is not a way to create a changing magnetic field?
Opening or closing a switch in a circuit, Moving a magnet relative to a circuit, and Moving a circuit relative to a magnet
Video 3: A cell phone emits EM waves at 1.9 GHz and a microwave oven emits EM waves at 2.4 GHz. Which one emits the shorter wavelength?
The microwave oven
An object is hung using a metal spring. If now a current is passed through the spring, what will happen to this system?
The spring will contract, raising the weight.
The equivalent capacitance of 2 capacitors connected in parallel is
The sum of the capacitances
What is the equivalent resistance when R1, R2, and R3 are all connected in parallel?
(1/R1 + 1/R2+ 1/R3)^-1
The parts of the electromagnetic spectrum that can ionize molecules and/or atoms are
Ultraviolet, x-rays and gamma rays
To measure the potential difference at a circuit element a voltmeter must be connected
In parallel with the element to be tested
To measure current in a circuit the ammeter must be connected
In series with the circuit elements
The Earth's magnetic north pole is
Near Earth's south geographic pole
How many time constants does it take to discharge a capacitor in an RC circuit?
Never fully discharged but 5 is accepted as the time it takes
Video 2: When the north pole of the magnet moves toward the copper a magnetic field is induced in the copper. What direction is the force between the copper and the magnet?
Repulsive
Which circuit element has a zigzag for its symbol?
Resistor
Kirchhoff's loop law
Says the potential difference around a loop is zero
In a circuit model of nerve-impulse propagation, what would happen to the propagation speed if the myalin sheath thickness were larger?
Speed would increase
Computer hard disks
Store data using magnetic fields
Changing the angle of a wire loop relative to a magnetic field changes
The magnetic flux
Faraday's law of electromagnetic induction helps determine
The magnitude of induced emfs and currents
In an electromagnetic wave in free space, the electric and magnetic fields are
perpendicular to one another and perpendicular to the direction of wave propagation
A flat coil is in a uniform magnetic field. The magnetic flux through the coil is greatest when the plane of its area is
perpendicular to the magnetic field.
Which one of the following lists gives the correct order of the electromagnetic waves from longer wavelength to shorter wavelength?
radio waves, microwaves, infrared, visible, ultraviolet, x-rays, gamma rays
Magnetic field lines point from
From north magnetic poles to south magnetic poles
What is the current in a circuit with a 10 V battery and 1000 ohms of resistance?
10 mA
A circuit consists of 1 battery and 2 identical resistors connected in parallel to the battery. The battery has an emf of 12 V. What is the potential difference across the first resistor?
12 V
A circuit consists of 1 battery and 2 identical resistors connected in series with the battery. The battery has an emf of 12 V. What is the potential difference across both resistors?
12 V
The equivalent resistance of 2 identical resistors with resistance R, which are connected in series is
2R
When two long parallel wires carry unequal currents, the magnitude of the magnetic force that one wire exerts on the other is F. If the current in both wires is now doubled, what is the magnitude of the new magnetic force on each wire?
4F
Induced current is current created by
A changing magnetic field
Two current carrying wires parallel to each other exert
A repulsive or attractive force depending on the directions of the currents
Several capacitors are connected in series with a battery. The potential difference across each capacitor
Adds to equal the emf of the battery
How are radio waves created?
An oscillating dipole causes an oscillating electric field which induces an oscillating magnetic field
Two parallel loops of wire with current in the same direction are near each other with an imaginary line connecting the centers of both loops and passing through the loops. What is the force between them?
Attractive
The electric field and magnetic field of an electromagnetic wave
Are perpendicular, Are in phase with each other, and Are related to the speed of light
Current in a wire creates a magnetic field
Around the wire
What magnetic field, B, is needed to create a motional emf for a conductor moving at speed v that is d long.
B = emf/vd
How does the magnetic field of a current carrying wire depend on the current, I, and the distance, r, from the wire?
B is proportional to I/r
Consider two current-carrying circular loops. Both are made from one strand of wire and both carry the same current, but one has twice the radius of the other. If the magnetic field strength at the center of the smaller loop is B, what is the magnetic field strength at the center of the larger loop?
B/4
The force needed to pull a wire along conducting rails in a magnetic field is proportional to
B^2
An electromagnetic flowmeter can be used to measure the velocity of
Blood and water
Magnetic domains are usually randomly oriented. This can be changed by
Bringing a magnet close to the sample
What is the equivalent capacitance for capacitors C1, C2, and C3 when they are connected in parallel?
C1+C2+C3
Cell walls can be modeled as what electric element(s)?
Capacitors and resistors
The auroras near Earth's north and south poles are created by
Charged particle from the sun interacting with Earth's magnetic field
Which animal has 4 types of cones in their eyes?
Chicken
Which element listed below is ferromagnetic?
Cobalt Nickel Iron
A changing electric field
Creates an induced magnetic field
Kirchhoff's junction law states that
Current into a junction is equal to current leaving it
The exponential behavior of an RC circuit occurs
During charging and discharging of the capacitor
Which of these equations is correct for the energy of a photon?
E = hf
What is the magnetic force, F, on a wire of length L carrying current I, in a magnetic field B?
F = ILB
RC circuits can be used for
Flashing lights on bicycles, Intermittent wipers on your car, and Timing in computers
What is the property of the copper in the track that leads to the braking force on the toy car?
Good electrical conductor
Refrigerator magnets
Have multiple poles arranged as long U-magnets
The induced current, I, due to an induced emf is
I = emf/R
The speed of an electromagnetic wave
Is equal to the speed of light
The magnetic field inside a current loop
Is in the opposite direction as the field outside the loop
The magnetic field of a solenoid
Is stronger inside the solenoid than outside
Several capacitors are connected in series with a battery. The charge on the capacitors
Is the same for each capacitor
How does the flash rate change for the light in the RC circuit when a larger resistor is put into the circuit?
It gets slower
Video 3: What property of the trash can blocks radio waves from getting to the radio?
It is a good electrical conductor
Two long, parallel wires carry currents of different magnitudes. If the current in one of the wires is doubled and the current in the other wire is halved, what happens to the magnitude of the magnetic force that each wire exerts on the other?
It stays the same.
The path of a charged object in a magnetic field depends on
Its mass Its velocity Its charge
What law describes the directions of eddy currents produced when a conductor moves through a magnetic field?
Lenz
Magnets attract
Magnetic materials
MRI's use what property of atoms to produce images?
Magnetic moment of the nucleus
A generator converts
Mechanical energy into electrical energy
The potential difference created by moving a conductor in a magnetic field is called
Motional emf
The induced current due to a changing magnetic flux produces a magnetic field which
Opposes the change of the flux
How are car headlights connected?
Parallel
The force on a moving charged object in a magnetic field is
Perpendicular to both the magnetic field and the object's velocity
The time constant for an RC circuit is
R*C
The equivalent resistance of 2 identical resistors, with resistance R, which are connected in parallel is
R/2
What is the equivalent resistance when R1, R2 and R3 are all connected in series?
R1+R2+R3
When current flows in a counterclockwise direction in a current loop the magnetic field created points to the left. What is the field direction when the current is reversed?
Right
What rule is used to determine the direction of the magnetic field created by a current moving in a wire?
Right hand rule
What rule is used to determine the force on a current carrying wire due to a magnetic field?
Right hand rule
You obtain a 100-W light bulb and a 50-W light bulb. Instead of connecting them in the normal way, you devise a circuit that places them in series across normal household voltage. If each one is an incandescent bulb of fixed resistance, which statement about these bulbs is correct?
The 50-W bulb glows more brightly than the 100-W bulb.
A resistor, an uncharged capacitor, a dc voltage source, and an open switch are all connected in series. The switch is closed at time t = 0 s. Which one of the following is a correct statement about this circuit?
The charge on the capacitor after four time constants is about 98% of the maximum value.
In a series circuit with 2 resistors
The current flows through one resistor then the next
In order for an electric motor to work
The current must change direction every half cycle
In a parallel resistor circuit with 2 resistors
The current splits and flows through both resistors at the same time
A current loop has a magnetic dipole moment equal to
The current times the area of the loop
Magnetic flux refers to how much magnetic field goes through a loop. The flux depends on the magnetic field and
The effective area of the loop
The polarization of electromagnetic waves refers to the orientation of
The electric field
Video 2: The circuit is constructed so that the blue LED comes on if the current is in one direction and the orange LED comes on if the current is in the other direction. The blue LED comes on when the magnet is quickly placed on the coil. As the magnet is quickly removed from the coil what will happen?
The orange LED comes on.
A photon is
The particle aspect of an electromagnetic wave
When two or more different capacitors are connected in parallel across a potential source (battery), which of the following statements must be true? (There could be more than one correct choice.)
The potential difference across each capacitor is the same. AND The capacitor with the largest capacitance has the most charge.
The magnetic field of a solenoid does not depend on
The radius of the solenoid
When two or more different capacitors are connected in series across a potential source, which of the following statements must be true? (There could be more than one correct choice.)
The total voltage across the combination is the algebraic sum of the voltages across the individual capacitors. AND Each capacitor carries the same amount of charge. AND The equivalent capacitance of the combination is less than the capacitance of any of the capacitors.
Video 3: Which laser pointer (red or violet) outputs the higher energy photons?
The violet laser
What direction is the magnetic force on a proton moving in the same direction as a magnetic field?
There is not force
When capacitors are connected in series
They have the same charge
When looking at the force on the wire with a current, which direction is the force on the wire when subjected to the south pole of the magnet? Current is to the left.
Toward the camera
Cutting a permanent magnet in half creates
Two weaker magnets
How do you determine the magnetic force on a negatively charged object moving through a magnetic field?
Use the right-hand rule and then reverse the direction of the force.
Which part of the electromagnetic spectrum listed below is the most particle like?
X-rays
When the switch is closed in the circuit shown in the figure, the wire between the poles of the horseshoe magnet deflects upward. From this you can conclude that the left end of the magnet is
a south magnetic pole.
A negatively-charged particle moves across a constant uniform magnetic field that is perpendicular to the velocity of the particle. The magnetic force on this particle
causes the particle to accelerate.
A coil lies flat on a level tabletop in a region where the magnetic field vector points straight up. The magnetic field suddenly grows stronger. When viewed from above, what is the direction of the induced current in this coil as the field increases?
clockwise
A bar magnet is oriented above a copper ring, as shown in the figure. If the magnet is pulled upward, what is the direction of the current induced in the ring, as viewed from above?
counterclockwise
An outer metal ring surrounds an inner metal ring, as shown in the figure. The current in the outer ring is counterclockwise and decreasing. What is the direction of the induced current in the inner ring?
counterclockwise
An electromagnetic wave is propagating towards the west in free space. At a certain moment the direction of the magnetic field vector associated with this wave points vertically upward. What is the direction of the electric field vector?
horizontal and pointing south
Kirchhoff's loop rule is a statement of
the law of conservation of energy.
Increasing the brightness of a beam of light without changing its color will increase
the number of photons per second traveling in the beam
