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{{Chapter 26Chapter 26

DC CircuitsDC Circuits

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Charging a capacitorCharging a capacitor

• The The time constanttime constant is is = RC = RC..

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Discharging a capacitorDischarging a capacitor

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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

Q26.8

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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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

A26.8

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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A battery, a capacitor, and a resistor are connected in series. Which of the following affect(s) the maximum charge stored on the capacitor?

Q26.9

A. the emf of the battery

B. the capacitance C of the capacitor

C. the resistance R of the resistor

D. both and C

E. all three of , C, and R

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A battery, a capacitor, and a resistor are connected in series. Which of the following affect(s) the maximum charge stored on the capacitor?

A26.9

A. the emf of the battery

B. the capacitance C of the capacitor

C. the resistance R of the resistor

D. both and C

E. all three of , C, and R

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{{Chapter 27Chapter 27

Magnetic Fields and ForcesMagnetic Fields and Forces

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Magnetic polesMagnetic poles

Figure 27.1 at the right Figure 27.1 at the right shows the forces between shows the forces between magnetic poles.magnetic poles.

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Magnetism and certain metalsMagnetism and certain metals Either pole of a Either pole of a

permanent permanent magnet will magnet will attract a metal attract a metal like iron, as like iron, as shown in Figure shown in Figure 27.2 at the right.27.2 at the right.

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Magnetic field of the earthMagnetic field of the earth The earth itself is a magnet. Figure 27.3 shows its magnetic field.The earth itself is a magnet. Figure 27.3 shows its magnetic field.

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Magnetic monopolesMagnetic monopoles

• Breaking a Breaking a bar magnet bar magnet does not does not separate its separate its poles, as poles, as shown in shown in Figure 27.4 Figure 27.4 at the right.at the right.

• There is no There is no experimentaexperimental evidence l evidence for for magnetic magnetic monopolesmonopoles..

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Electric current and magnetsElectric current and magnets• In 1820, Hans In 1820, Hans

Oersted discovered Oersted discovered that a current-that a current-carrying wire causes carrying wire causes a compass to deflect. a compass to deflect. (See Figure 27.5 at (See Figure 27.5 at the right.) the right.)

• This discovery This discovery revealed a connection revealed a connection between moving between moving charge and charge and magnetism.magnetism.

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Magnetic force as a vector productMagnetic force as a vector product• We can write the magnetic force as a vector product We can write the magnetic force as a vector product

(see Figure 27.7 below).(see Figure 27.7 below).• The right-hand rule gives the direction of the force on a The right-hand rule gives the direction of the force on a

positivepositive charge. charge.

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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 from the magnet points straight down. Which way will the electron beam deflect?

A. upward

B. downward

C. to the left

D. to the right

E. It won’t deflect at all.

A27.1

B

B

N

Beam of electrons coming toward you

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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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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

Q27.3

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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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

A27.3

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 calculationsMagnetic 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