Q78P-f We will consider the possibility... [FREE SOLUTION]

The center of a bar magnet whose magnetic dipole moment is $〈 8, 0, 0 〉 A \cdot m^{2}$ is located at the origin. A second bar magnet whose magnetic dipole moment is $〈 3, 0, 0 〉 A \cdot m^{2}$ is located at $x = 0 .12 m$ . What is the vector force on the second magnet due to the first magnet?

We will consider the possibility that a free electron actedon by an electric field could gain enough energy to ionize anair molecule in a collision. (a) Consider an electron that startsfrom rest in a region where there is an electric field (due to somecharged objects nearby) whose magnitude is nearly constant. Ifthe electron travels a distance $d$ and the magnitude of the electric field is $E$ ,what isthe potential difference through which the electron travels? (Pay attention to signs: Is the electron traveling with the electric field or opposite to the electric field?) (b) What is the change in potential energy of the system in this process? (c) What is the change in the kinetic energy of the electron in this process? (d) We found the mean free path of an electron in air to be about $5 \times 10^{- 7} m$ , and in the previous question you calculated the energy required to knock an electron out of an atom. What is the magnitude of the electric field that would be required in order for an electron to gain sufficient kinetic energy to ionize a nitrogen molecule? (e) The electric field required to cause a spark in air is observed to be about $3 \times 10^{6} V/m$ at STP. What is the ratio of the magnitude of the field you calculated in the previous part to the observed value at STP? (f) What is it reasonable to conclude about this model of how air becomes ionized? (1) Since we used accurate numbers, this is a huge discrepancy, and the model is wrong. (2) Considering the approximations we made, this is pretty good agreement, and the model may be correct.

A metal rod of length L slides horizontally at constant speed v on frictionless insulating rails through a region of uniform upward magnetic field of magnitude B (Figure 20.124).

On a diagram, show the polarization of the rod and the direction of the Coulomb electric field inside the rod. Explain briefly. What is the magnitude of the Coulomb electric field inside the rod? What is the potential difference across the rod? What is the emf across the rod? What are the magnitude and direction of the force you have to apply to keep the rod moving at a constant speed v?

:In Figure 20.121 a bar 11 cm long with a rectangular cross section 3 cm high and 2 cm deep is connected to a 1.2 V battery and an ammeter. The resistance of the copper connecting wires and the ammeter, and the internal resistance of the battery, are all negligible compared to the resistance of the bar.

Using large coils not shown on the diagram, a uniform magnetic field of 1.8 T was applied perpendicular to the bar (out of the page, as shown). A voltmeter was connected across the bar, with the connections across the bar carefully placed directly across from each other.

The mobile charges in the bar have charge +e, their density is $7 \times 10^{23} / m^{3}$ , and their mobility is $3 \times 10^{- 5} (m/s) / (V/m)$ .

Predict the readings of the voltmeter and ammeter, including signs. Explain carefully, using diagrams to support your explanation. Remember that a voltmeter reads positive if the + terminal is connected to higher potential, and that an ammeter reads positive if conventional current enters the + terminal.

A neutral metal rod of length 60 cm falls toward the Earth. The rod is horizontal and oriented east west. (1) Which end of the rod, east or west, has excess electrons? Explain using physics diagrams. (2) At a moment when the rod’s speed is 4m/s , approximately how many excess electrons are at the negative end of the rod?

Short Answer

Step by step solution

Identification of given data

Significance of electric field

(f) Determining that it is reasonable to conclude about this model of how air becomes ionized

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