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physics
modern physics
Questions and Answers of
Modern Physics
A solenoid is formed by winding 25.0 m of insulated silver wire around a hollow cylinder. The turns are wound as closely as possible without overlapping, and the insulating coat on the wire is
The figure shows two parallel, straight wires that are very long. The wires are separated by a distance of 0.065 m and carry currents of I1 = 15 A and I2 = 7.0 A. Find the magnitude and direction of
The figure shows a particle that carries a charge of q0 = -2.80 Ã 10-6 C. It is moving along the +y axis at a speed of v = 4.8 Ã 106 m/s. A magnetic field of magnitude 3.35
A 125-turn rectangular coil of wire is hung from one arm of a balance, as the figure shows. With the magnetic field turned off, an object of mass M is added to the pan on the other arm to balance the
The drawing shows a parallel plate capacitor that is moving with a speed of 32 m/s through a 3.6-T magnetic field. The velocity is perpendicular to the magnetic field. The electric field within the
You have a fixed length of conducting wire. From it you can construct a single-turn flat coil that has the shape of a square, a circle, or a rectangle with the long side twice the length of the short
An electric motor is plugged into a standard wall socket and is running at normal speed. Suddenly, some dirt prevents the shaft of the motor from turning quite so rapidly. What happens to the back
Inductor 1 stores the same amount of energy as inductor 2, although it has only one-half the inductance of inductor 2. What is the ratio I1/I2 of the currents in the two inductors? (a) 2.000 (b)
The primary coil of a step-up transformer is connected across the terminals of a standard wall socket, and resistor 1 with a resistance R1 is connected across the secondary coil. The current in the
You have three light bulbs; bulb A has a resistance of 240 Ω, bulb B has a resistance of 192 Ω, and bulb C has a resistance of 144 Ω. Each of these bulbs is used for the same amount of time in a
The drawing shows a cube. The dashed lines in the drawing are perpendicular to faces 1, 2, and 3 of the cube. Magnetic fields are oriented with respect to these faces as shown, and each of the three
The drawing shows three fl at coils, one square and two rectangular, that are each being pushed into a region where there is a uniform magnetic field directed into the page. Outside of this region
A long, vertical, straight wire carries a current I. The wire is perpendicular to the plane of a circular metal loop and passes through the center of the loop (see the drawing). The loop is allowed
The drawing shows a top view of two circular coils of conducting wire lying on a flat surface. The centers of the coils coincide. In the larger coil there are a switch and a battery. The smaller coil
A 0.80-m aluminum bar is held with its length parallel to the east-west direction and dropped from a bridge. Just before the bar hits the river below, its speed is 22 m/s, and the emf induced across
Review Conceptual Example 3 and Figure 22.7b. A conducting rod slides down between two frictionless vertical copper tracks at a constant speed of 4.0 m/s perpendicular to a 0.50-T magnetic field. The
Two fl at surfaces are exposed to a uniform, horizontal magnetic field of magnitude 0.47 T. When viewed edge-on, the first surface is tilted at an angle of 12° from the horizontal, and a net
A loop of wire has the shape shown in the drawing. The top part of the wire is bent into a semicircle of radius r = 0.20 m. The normal to the plane of the loop is parallel to a constant magnetic
A magnetic field has a magnitude of 0.078 T and is uniform over a circular surface whose radius is 0.10 m. The field is oriented at an angle of ϕ = 25° with respect to the normal to the surface.
A square loop of wire consisting of a single turn is perpendicular to a uniform magnetic field. The square loop is then re-formed into a circular loop, which also consists of a single turn and is
A five-sided object, whose dimensions are shown in the drawing, is placed in a uniform magnetic field. The magnetic field has a magnitude of 0.25 T and points along the positive y direction.
A magnetic field passes through a stationary wire loop, and its magnitude changes in time according to the graph in the drawing. The direction of the field remains constant, however. There are three
A rectangular loop of wire with sides 0.20 and 0.35 m lies in a plane perpendicular to a constant magnetic field (see part a of the drawing). The magnetic field has a magnitude of 0.65 T and is
Near San Francisco, where the vertically downward component of the earth's magnetic field is 4.8 × 10-5 T, a car is traveling forward at 25 m/s. The width of the car is 2.0 m. (a) Find the emf
Magnetic resonance imaging (MRI) is a medical technique for producing pictures of the interior of the body. The patient is placed within a strong magnetic field. One safety concern is what would
The magnetic flux that passes through one turn of a 12-turn coil of wire changes to 4.0 from 9.0 Wb in a time of 0.050 s. The average induced current in the coil is 230 A. What is the resistance of
A constant magnetic field passes through a single rectangular loop whose dimensions are 0.35 m × 0.55 m. The magnetic field has a magnitude of 2.1 T and is inclined at an angle of 65° with respect
A uniform magnetic field is perpendicular to the plane of a single-turn circular coil. The magnitude of the field is changing, so that an emf of 0.80 V and a current of 3.2 A are induced in the coil.
A copper rod is sliding on two conducting rails that make an angle of 19° with respect to each other, as in the drawing. The rod is moving to the right with a constant speed of 0.60 m/s. A 0.38-T
A flat coil of wire has an area A, N turns, and a resistance R. It is situated in a magnetic field, such that the normal to the coil is parallel to the magnetic field. The coil is then rotated
A flat circular coil with 105 turns, a radius of 4.00 × 10-2 m, and a resistance of 0.480 Ω is exposed to an external magnetic field that is directed perpendicular to the plane of the coil. The
The drawing shows a coil of copper wire that consists of two semicircles joined by straight sections of wire. In part a the coil is lying fl at on a horizontal surface. The dashed line also lies in
In 1996, NASA performed an experiment called the Tethered Satellite experiment. In this experiment a 2.0 × 104-m length of wire was let out by the space shuttle Atlantis to generate a motional emf.
A conducting coil of 1850 turns is connected to a galvanometer, and the total resistance of the circuit is 45.0 Ω. The area of each turn is 4.70 × 10-4 m2. This coil is moved from a region where
Starting from the position indicated in the drawing, the semicircular piece of wire rotates through half a revolution in the direction shown. Which end of the resistor is positive-the left or the
The drawing shows a straight wire carrying a current I. Above the wire is a rectangular loop that contains a resistor R. If the current I is decreasing in time, what is the direction of the induced
The drawing shows that a uniform magnetic field is directed perpendicularly into the plane of the paper and fills the entire region to the left of the y axis. There is no magnetic field to the right
A circular loop of wire rests on a table. A long, straight wire lies on this loop, directly over its center, as the drawing illustrates. The current I in the straight wire is decreasing. In what
The drawing shows a bar magnet falling through a metal ring. In part a the ring is solid all the way around, but in part b it has been cut through.(a) Explain why the motion of the magnet in part a
A wire loop is suspended from a string that is attached to point P in the drawing. When released, the loop swings downward, from left to right, through a uniform magnetic field, with the plane of the
The drawing shows a type of flow meter that can be used to measure the speed of blood in situations when a blood vessel is sufficiently exposed (e.g., during surgery). Blood is conductive enough that
A 120.0-V motor draws a current of 7.00 A when running at normal speed. The resistance of the armature wire is 0.720 Ω. (a) Determine the back emf generated by the motor. (b) What is the current at
You need to design a 60.0-Hz ac generator that has a maximum emf of 5500 V. The generator is to contain a 150-turn coil that has an area per turn of 0.85 m2. What should be the magnitude of the
The maximum strength of the earth's magnetic field is about 6.9 × 10-5 T near the south magnetic pole. In principle, this field could be used with a rotating coil to generate 60.0-Hz ac electricity.
A vacuum cleaner is plugged into a 120.0-V socket and uses 3.0 A of current in normal operation when the back emf generated by the electric motor is 72.0 V. Find the coil resistance of the motor.
A generator uses a coil that has 100 turns and a 0.50-T magnetic field. The frequency of this generator is 60.0 Hz, and its emf has an rms value of 120 V. Assuming that each turn of the coil is a
The coil of a generator has a radius of 0.14 m. When this coil is unwound, the wire from which it is made has a length of 5.7 m. The magnetic field of the generator is 0.20 T, and the coil rotates at
A motor is designed to operate on 117 V and draws a current of 12.2 A when it first starts up. At its normal operating speed, the motor draws a current of 2.30 A. Obtain (a) The resistance of the
The current through a 3.2-mH inductor varies with time according to the graph shown in the drawing. What is the average induced emf during the time intervals(a) 0-2.0 ms,(b) 2.0-5.0 ms, and(c)
Two coils of wire are placed close together. Initially, a current of 2.5 A exists in one of the coils, but there is no current in the other. The current is then switched off in a time of 3.7 × 10-2
During a 72-ms interval, a change in the current in a primary coil occurs. This change leads to the appearance of a 6.0-mA current in a nearby secondary coil. The secondary coil is part of a circuit
Mutual induction can be used as the basis for a metal detector. A typical setup uses two large coils that are parallel to each other and have a common axis. Because of mutual induction, the ac
A constant current of I = 15 A exists in a solenoid whose inductance is L = 3.1 H. The current is then reduced to zero in a certain amount of time. (a) If the current goes from 15 to 0 A in a time of
Suppose you wish to make a solenoid whose self-inductance is 1.4 mH. The inductor is to have a cross-sectional area of 1.2 × 10-3 m2 and a length of 0.052 m. How many turns of wire are needed?
A long, current-carrying solenoid with an air core has 1750 turns per meter of length and a radius of 0.0180 m. A coil of 125 turns is wrapped tightly around the outside of the solenoid, so it has
A 5.40 × 10-5 H solenoid is constructed by wrapping 65 turns of wire around a cylinder with a cross sectional area of 9.0 × 10-4 m2. When the solenoid is shortened by squeezing the turns closer
A long solenoid (cross-sectional area = 1.0 × 10-6 m2, number of turns per unit length = 2400 turns/m) is bent into a circular shape so it looks like a donut. This wire-wound donut is called a
Coil 1 is a fl at circular coil that has N1 turns and a radius R1. At its center is a much smaller flat, circular coil that has N2 turns and radius R2. The planes of the coils are parallel. Assume
Two circuits contain an emf produced by a moving metal rod, like that shown in Figure 22.4b. The speed of the rod is the same in each circuit, but the bulb in circuit 1 has one-half the resistance of
The battery charger for an MP3 player contains a step-down transformer with a turns ratio of 1:32, so that the voltage of 120 V available at a wall socket can be used to charge the battery pack or
The secondary coil of a step-up transformer provides the voltage that operates an electrostatic air filter. The turns ratio of the transformer is 50:1. The primary coil is plugged into a standard
The rechargeable batteries for a laptop computer need a much smaller voltage than what a wall socket provides. Therefore, a transformer is plugged into the wall socket and produces the necessary
The resistances of the primary and secondary coils of a transformer are 56 and 14 Ω, respectively. Both coils are made from lengths of the same copper wire. The circular turns of each coil have the
A transformer consisting of two coils wrapped around an iron core is connected to a generator and a resistor, as shown in the drawing. There are 11 turns in the primary coil and 18 turns in the
In a television set the power needed to operate the picture tube comes from the secondary of a transformer. The primary of the transformer is connected to a 120-V receptacle on a wall. The picture
Suppose there are two transformers between your house and the high-voltage transmission line that distributes the power. In addition, assume that your house is the only one using electric power. At a
A generator is connected across the primary coil (Np turns) of a transformer, while a resistance R2 is connected across the secondary coil (Ns turns). This circuit is equivalent to a circuit in which
Refer to the drawing that accompanies Check Your Understanding Question 14. Suppose that the voltage of the battery in the circuit is 3.0 V, the magnitude of the magnetic field (directed
In each of two coils the rate of change of the magnetic flux in a single loop is the same. The emf induced in coil 1, which has 184 loops, is 2.82 V. The emf induced in coil 2 is 4.23 V. How many
A planar coil of wire has a single turn. The normal to this coil is parallel to a uniform and constant (in time) magnetic field of 1.7 T. An emf that has a magnitude of 2.6 V is induced in this coil
In some places, insect "zappers," with their blue lights, are a familiar sight on a summer's night. These devices use a high voltage to electrocute insects. One such device uses an ac voltage of 4320
At its normal operating speed, an electric fan motor draws only 15.0% of the current it draws when it just begins to turn the fan blade. The fan is plugged into a 120.0-V socket. What back emf does
Parts a and b of the drawing show the same uniform and constant (in time) magnetic field directed perpendicularly into the paper over a rectangular region. Outside this region, there is no field.
Indicate the direction of the electric field between the plates of the parallel plate capacitor shown in the drawing if the magnetic field is decreasing in time. Give your reasoning.
Multiple-Concept Example 2 discusses the concepts that are used in this problem. Suppose that the magnetic field in Figure 22.5 has a magnitude of 1.2 T, the rod has a length of 0.90 m, and the hand
The purpose of this problem is to show that the work W needed to establish a final current If in an inductor is W = 1/2 LI2f (Equation 22.10). In Section 22.8 we saw that the amount of work
A solenoid has a cross-sectional area of 6.0 × 10-4 m2, consists of 400 turns per meter, and carries a current of 0.40 A. A 10-turn coil is wrapped tightly around the circumference of the solenoid.
A 60.0-Hz generator delivers an average power of 75 W to a single light bulb. When an induced current exists in the rotating coil of a generator, a torque-called a countertorque-is exerted on the
A circular coil of radius 0.11 m contains a single turn and is located in a constant magnetic field of magnitude 0.27 T. The magnetic field has the same direction as the normal to the plane of the
The graph in the figure shows the emf produced by a generator as a function of time t. The coil for the generator has an area of A = 0.15 m2 and consists of N = 10 turns. The coil rotates in a field
A circuit contains an ac generator and a resistor. What happens to the average power dissipated in the resistor when the frequency is doubled and the rms voltage is tripled? (a) Nothing happens,
A capacitor and an inductor are connected to an ac generator in two ways: in series and in parallel (see the drawing). At low frequencies, which circuit has the greater current? (a) The series
In an RCL circuit a second capacitor is added in parallel to the capacitor already present. Does the resonant frequency of the circuit increase, decrease, or remain the same? (a) The resonant
What happens to the capacitive reactance XC and the inductive reactance XL if the frequency of the ac voltage is doubled? (a) XC increases by a factor of 2, and XL decreases by a factor of
An inductor has an inductance of 0.080 H. The voltage across this inductor is 55 V and has a frequency of 650 Hz. What is the current in the inductor?
An inductor is to be connected to the terminals of a generator (rms voltage = 15.0 V) so that the resulting rms current will be 0.610 A. Determine the required inductive reactance.
An ac generator has a frequency of 7.5 kHz and a voltage of 39 V. When an inductor is connected between the terminals of this generator, the current in the inductor is 42 mA. What is the inductance
A 40.0-µF capacitor is connected across a 60.0-Hz generator. An inductor is then connected in parallel with the capacitor. What is the value of the inductance if the rms currents in the inductor and
An ac generator has a frequency of 2.2 kHz and a voltage of 240 V. An inductance L1 = 6.0 mH is connected across its terminals. Then a second inductance L2 = 9.0 mH is connected in parallel with L1.
Two inductors are connected in parallel across the terminals of a generator. One has an inductance of L1 = 0.030 H, and the other has an inductance of L2 = 0.060 H. A single inductor, with an
A series RCL circuit contains a 47.0-Ω resistor, a 2.00-µF capacitor, and a 4.00-mH inductor. When the frequency is 2550 Hz, what is the power factor of the circuit?
Two identical capacitors are connected in parallel to an ac generator that has a frequency of 610 Hz and produces a voltage of 24 V. The current in the circuit is 0.16 A. What is the capacitance of
An ac series circuit has an impedance of 192 V, and the phase angle between the current and the voltage of the generator is ϕ = -75°. The circuit contains a resistor and either a capacitor or an
When only a resistor is connected across the terminals of an ac generator (112 V) that has a fixed frequency, there is a current of 0.500 A in the resistor. When only an inductor is connected across
A 2700-Ω resistor and a 1.1-µF capacitor are connected in series across a generator (60.0 Hz, 120 V). Determine the power delivered to the circuit.
Suppose that the inductance is zero (L = 0H) in the series RCL circuit shown in Figure 23.10. The rms voltages across the generator and the resistor are 45 and 24 V, respectively. What is the rms
Part a of the drawing shows a resistor and a charged capacitor wired in series. When the switch is closed, the capacitor discharges as charge moves from one plate to the other. Part b shows the
In one measurement of the body's bioelectric impedance, values of Z = 4.50 × 102 V and ϕ = -9.80° are obtained for the total impedance and the phase angle, respectively. These values assume that
A series RCL circuit contains only a capacitor (C = 6.60 µF), an inductor (L = 7.20 mH), and a generator (peak voltage = 32.0 V, frequency = 1.50 × 103 Hz). When t = 0 s, the instantaneous value of
An 84.0-mH inductor and a 5.80-µF capacitor are connected in series with a generator whose frequency is 375 Hz. The rms voltage across the capacitor is 2.20 V. Determine the rms voltage across the
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