Transcript RC Circuits and Intro to Magnetism (7/8)

Chapter 26
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DC Circuits
Charging a capacitor
•
The time constant is  = RC.
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Discharging a capacitor
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Q26.8
You wish to study a resistor in a circuit. To simultaneously
measure the current in the resistor and the voltage across the
resistor, you would place
A. an ammeter in series and an voltmeter in series.
B. an ammeter in series and an voltmeter in parallel.
C. an ammeter in parallel and an voltmeter in series.
D. an ammeter in parallel and an voltmeter in parallel.
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A26.8
You wish to study a resistor in a circuit. To simultaneously
measure the current in the resistor and the voltage across the
resistor, you would place
A. an ammeter in series and an voltmeter in series.
B. an ammeter in series and an voltmeter in parallel.
C. an ammeter in parallel and an voltmeter in series.
D. an ammeter in parallel and an voltmeter in parallel.
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Q26.9
A battery, a capacitor, and a resistor are connected in series.
Which of the following affect(s) the maximum charge stored
on the capacitor?
A. the emf e of the battery
B. the capacitance C of the capacitor
C. the resistance R of the resistor
D. both e and C
E. all three of e, C, and R
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A26.9
A battery, a capacitor, and a resistor are connected in series.
Which of the following affect(s) the maximum charge stored
on the capacitor?
A. the emf e of the battery
B. the capacitance C of the capacitor
C. the resistance R of the resistor
D. both e and C
E. all three of e, C, and R
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Chapter 27
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Magnetic Fields and Forces
Magnetic poles

Figure 27.1 at the right shows
the forces between magnetic
poles.
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Magnetism and certain metals

Either pole of a
permanent magnet
will attract a metal
like iron, as shown
in Figure 27.2 at
the right.
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Magnetic field of the earth

The earth itself is a magnet. Figure 27.3 shows its magnetic field.
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Magnetic monopoles
•
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Breaking a bar
magnet does
not separate
its poles, as
shown in
Figure 27.4 at
the right.
There is no
experimental
evidence for
magnetic
monopoles.
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Electric current and magnets
•
•
In 1820, Hans Oersted
discovered that a
current-carrying wire
causes a compass to
deflect. (See Figure 27.5
at the right.)
This discovery revealed
a connection between
moving charge and
magnetism.
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Magnetic force as a vector product
•
•
We can write the magnetic force as a vector product (see Figure
27.7 below).
The right-hand rule gives the direction of the force on a positive
charge.
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A27.1
A beam of electrons (which have negative charge q)
is coming straight toward you. You put the north
pole of a magnet directly above the beam. The
magnetic field B from the magnet points straight
down. Which way will the electron beam deflect?
N
B
A. upward
B. downward
C. to the left
D. to the right
E. It won’t deflect at all.
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Beam of electrons
coming toward you
Q27.2
When a charged particle moves through a magnetic field, the
direction of the magnetic force on the particle at a certain point is
A. in the direction of the magnetic field at that point.
B. opposite to the direction of the magnetic field at that point.
C. perpendicular to the magnetic field at that point.
D. none of the above
E. One of A or B above, depending on the sign of the particle’s
electric charge.
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A27.2
When a charged particle moves through a magnetic field, the
direction of the magnetic force on the particle at a certain point is
A. in the direction of the magnetic field at that point.
B. opposite to the direction of the magnetic field at that point.
C. perpendicular to the magnetic field at that point.
D. none of the above
E. One of A or B above, depending on the sign of the particle’s
electric charge.
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Q27.3
A particle with a positive
charge moves in the xz-plane
as shown. The magnetic field
is in the positive z-direction.
The magnetic force on the
particle is in
A. the positive x-direction.
B. the negative x-direction.
C. the positive y-direction.
D. the negative y-direction.
E. none of these
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A27.3
A particle with a positive
charge moves in the xz-plane
as shown. The magnetic field
is in the positive z-direction.
The magnetic force on the
particle is in
A. the positive x-direction.
B. the negative x-direction.
C. the positive y-direction.
D. the negative y-direction.
E. none of these
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Magnetic flux calculations
• Example – calculate field strength of constant magnetic field
through surface with area 3.0 cm2 if total magnetic flux is 0.90 mWb
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