Electricity and Magnetism Answers

Gauss's law combines the electric field over a surface with the area of the surface. From Coulomb's law we know that the electric field falls off as  1/r^2 of the distance r from the charge. How does the surface area change with r?

a.1/r

b.1/r^2

c.r^2

d.ln r

Tiny sensors in smartphone could be used to determine the position of the phone on 

the Earth’s surface by measuring the Earth’s magnetic field. A current I is applied to a 

slice of semiconductor as shown in Figure 1(a).

After detecting magnetic field, Bexternal of 2.55 mT on the slice, the electrons collect at 

the top edge of the slice and the bottom edge becomes positively charged as shown in 

Figure 1(b).

(a) Explain why the electrons collect at the top of the edge of the slice.

(b) Determine the magnitude of the maximum magnetic force that could be exerted on 

the electron if the electron moves through the field with a speed of 5.5 × 106 m s

−1

A proton is moving in the positive x-direction as shown in Figure 2 with a speed of 1.25 × 106 m s −1 . Then, the proton enters the region between the two plates. The potential difference between the plates is 200 V. The electric potential of the upper plate is higher than the electric potential of the lower plate. The separation distance between the plates is 35.0 mm. Determine the direction and the magnitude of the magnetic field that is required between the plates for the proton to continue traveling in a straight line in the positive x-direction.

2 charged particles reacted with a force of 0.31 N with a distance of 1.5 cm, the 2nd charge contains 54 nC. Find the value of the first charge.

Figure 2 below show cross section of two long straight wire separated by distance 0.5 m. Wire 2 carries current 2.0 A directed into the page. Determine the magnitude and direction (into or out of the page) of the current in wire 1 if the resultant of the magnetic field due to the two wire is zero at point Q located 0.8m from wire 2. Sketch diagram to prove your answer.

The magnetic field strength at the center of a circular coil with N turns is B. If the number of turns is double but the current and radius are each half, the magnetic field strength at the center would be 

explain

why the electrons collect at the top of the edge of the slice that related to the attraction upward,V and B?

FIGURE 1 shows two long parallel wires 2 cm apart. Wire P carries a current 7 A to

the right. Point C is 3 cm from wire Q and in the same plane as wire P and Q.

Determine the magnitude and direction of current in wire Q so that the magnetic field

at C is zero.

The ratio of number of electronic states in the energy range 2-3 eV to that of in 0-3 eV ((Number of electronic states in the energy range 2 -3 eV)/(Number of electronic states in the energy range 0-3 eV)) will be

What is the magnitude of the electric force between two electrons

separated by a distance of 0.10 nm? (1 nm = 1 x 10 -9 m)