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A 0.1g plastic bead is charged by the addition of 10^10 excess electrons. what electric field E( strength and direction ) will cause the bead to hang suspended in the air ?

• 25 N/C, upward

• 62500 N/C, downward

• 625 N/C, downward

• 2500 N/C, downward

two long, parallel are seperated by a distance of 0.400. One wire has 5A current, and the other has 2 A running in the opposite directon. Caculate the magnitude of the force exerted by each wire on a 1.20m length of the other.

• 6 micro Newton

• 3 micro Newton

• 12 micro Newton

• 1 micro Newton

the magnetic field at the center of a 1.0cm diameter loop is 2.5mt. What is the current in the loop ?

• 0

• 10 A

• 25 A

• 20 A

two identical metaal spheres A and B are connected by a plastic rod. Both are intially neutral. 10^12 electrons are added to sphere A. Then the connecting rod is removed. Afterward, what are the charge of A and the charge of B ?

• A has 0 nC,; B has -160 C

• Both has 0 C

• A and B has -80 nC each

• A has -160 nC; B has 0 C

What is the electric potential at point P, located at the center of the square of charged particles shown in the figure ? The distance d is 1.3m, and the charges are q_1 = +12nC, q_2 = -24nC, q3=31nC, and q_4 = +17nC.

• 249V

• 384V

• 192V

• 353V

The figure shows a long solenoid S shown (in cross section) which has

220 turns/cm and carries a current i = 1.5 A; its diameter D

is 3.2 cm. At its center we place a 130-turn closely packed

coil C of diameter d = 2.1 cm.

(a) What is the flux of the magnetic field through coil C. The current in the solenoid is reduced to zero at a steady rate in 25 ms.

(b)What is the magnitude of the EMF that is induced in coil C while the current in

the solenoid is changing?

A 2.40-cm-tall object is 60.0 cm to the left of a converging lens of focal length 40.0 cm. A second converging lens, this one having a focal length of 60.0 cm, is located 300.0 cm to the right of the first lens along the same optic axis. What are the nature and orientation of the final image produced by the combination of lenses?

• Virtual and erect

• Real and inverted

• Virtua land inverted

• Real and erect

Two satellites at an altitude of 1200 km are separated by 32 km. If they broadcast 3.6 cm microwaves, what minimum receiving-dish diameter is needed to resolve (by Rayleigh’s criterion) the two transmissions?

• 1.647 m

• 0.904 m

• 1.350 m

• 0.741 m