Physics Answers

1.Consider the electric flux Φ E=E⋅A of a uniform electric field (whose magnitude is E

) that makes an angle θ with the unit vector n that is normal to a rectangular surface whose area is A. Then the electric flux ΦE can be shown to be equal to:

a. 0

b. EA

c. EA n

d. EA cos θ

2.The flux ϕE=28N⋅m^2/C through the open surface A=6i+10j+5k is given. Find the value of a if the electric field is E=−ai +8k Value of "a"

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

Determine the magnitude of an electric field at r=0.01 m from the center of non-conducting sphere with a radius of R=0.001m possessing a charge of 7C which evenly distributed throughout the sphere. (r>R).

Solve for the electric flux that acts on a uniform electric field with a magnitude of 8000N/C approximately passes through a 10m^2 flat surface area.

a molecules of oxygen possess a charges of -2C and 2C separated from a distance of 0.2m. Calculate the dipole moment in this condition.

Water enters the heater at 30oC and leaves at 150oF, what is the temperature difference in oC?

The depth of the crater of a Volcano was calculated in the following manner. From a helicopter flying vertically upwards at 20 feet per second, a small bomb was released at the instant the helicopter was 120 feet above the crater surface. The sound of the explosion was heard 9 seconds later. The speed of the sound is 1000 fps. What is the depth of the crater in feet?

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

The elevator in an office building, starting from rest at the first floor, is accelerated 0.75 m/sec2 for 5 secs. It continues at constant velocity for 12 secs more and is then stopped in 3 secs with constant deceleration. If the floors are 3.75m apart, at what floor did the elevator stop?

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.