Biophysics II exam I

How much kinetic energy does a proton gain if it is accelerated, with no friction, through a potential difference of 1V? The proton is 1836 times heavier than an electron

1 eV

Two 5uC point charges are 12cm apart. what is the electric potential of this combination at the point where the electric field due to these charges is zero

1.5MV

Two identical small charged spheres are a certain distance apart, and each one initially experiences an electrostatic force of magnitude F due to the other. With time, charge gradually diminishes on both spheres by leaking off. When each spheres has lost half its initial charge, what will be the magnitude of the electrostatic force on each one?

1/4 F

How much work is needed to carry an electron from the positive terminal to the negative terminal of a 9V battery

14.4x10^-19

As shown in the figure, three charges are at the vertices of an equilateral triangle. the charge Q is 6.7 nC, and all other quantities are accurate to two sig figs. What is the magnitude of the net electric force on the charge Q due to the other two charges?

2.1x10^-3

If an electron is accelerated from rest through a potential difference of 1500 V, what speed does it reach?

2.3x10^7

two ideal parallel-plate capacitors are identical in every respect except that one has twice the plate area of the other. If the smaller capacitor has a capacitance of C the larger one has capacitance

2C

A capacitor charged to 3V stores 8mJ of energy. If the capacitor is charged to 1.5V, it will store

2mJ

The force of attraction that a -40 uC point charge exerts on a +108 uC point charge has a magnitude of 4.00 N. How far apart are these two charge?

3.12 m

You are given a copper bar of dimensions 3 cm × 5 cm × 8 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the largest possible resistance, you should attach the leads to the opposite faces that measure

5 cm x 8 cm

How many electrons are necessary to produce 1 C of negative charge?

6.3x10^18

A particle of charge +2q is placed at the origin, and a particle of charge -q is placed on the x-axis at x=2a. Where on the x-axis can a third positive charge be placed so that the net electric force on it is zero?

6.8a

Which one of the arrows shown in the figure best represents the direction of the electric field between the two uniformly charged metal plates?

A

Which is the direction of the net force on the charge at the lower left?

B

Two identical positive charges are placed near each other. At the point halfway between the two charges,

E-field is zero and the potential is positive

Which of the following do not affect the capacitance?

Energy stored in the capacitor

Metal spheres 1 and 2 are touching. Both are initially neutral. a. The charged rod is brought near. b. The spheres are separated. c. the charged rod is then removed, Afterward, the charges on the sphere are:

Q1 is - and Q2 is +

A hydrogen nucleus which has a charge +e, is situated to the left of a carbon nucleus, which has a charge +6e. Which statement is true?

The electrical force experienced by the hydrogen nucleus is to the left, and the magnitude is equal to the force exerted on the carbon nucleus.

Copper wire #1 has a length L and a radius b. Copper wire #2 has a length 2L and a radius 2b. Which statement about the resistance across the ends of the wires is true?

The resistance of wire #1 is twice as high as that of wire #2

Wire 2 is twice the length and twice the diameter of wire 1. They are made up of the same material. What is the ratio of their resistivity?

1

If the result of your calculation of a quantity has SI units kg • m2/(s2 • C), that quantity could b

an electric field strength

Doubling the capacitance of a capacitor that is holding a constant charge causes the energy stored in that capacitor to

decrease to one half

An capacitor consists of two large parallel plates of area A separated by a very small distance d. This capacitor is connected to a battery and charged until its plates carry charges +Q and -Q, and then disconnected from the battery. If the separation between the plates is now doubled, the potential difference between the plates will A) double. B) quadruple. C) be cut in half. D) be cut in fourth. E) not change.

double

The electron-volt is a unit of

energy

a hydrogen atom consist of a proton and an electron. If the orbital radius of the electron increases, the electric potential energy of the electron due to the proton

increases

The length of a certain wire is doubled and at the same time its radius is also doubled. What is the new resistance of this wire

it is 1/2 as large

Two point charges, Q1 and Q2, are separated by a distance R. If the magnitudes of both charges are doubled and their separation is also doubled, what happens to the electrical force that each charge exerts on the other one?

it remains the same

Two point charges, Q1 and Q2, are separated by a distance R. If the magnitudes of both charges are halved and their separation is also halved, what happens to the electrical force that each charge exerts on the other one?

it remains the same

For the graph shown in the figure, what physical quantity does the slope of the graph represent for ohmic material?

resistance

An electron is initially moving to the right when it enters a uniform electric field directed upwards, as shown in the figure. Which trajectory will the electron follow in the field?

trajectory Z