Electrostatics and Magnetism- MCAT
(See picture #101) Why does the vertical deflector not cause horizontal movement? A. Horizontal lines are equipotential when only the vertical deflector is active. B. The horizontal deflector counters any horizontal movement C. Vertical acceleration is too significant to allow horizontal movement D. The vertical deflector does cause some deviation horizontally.
A. The electric field lines when the vertical deflector is active are vertical between the two plates. Since they are parallel to one another, any line that is perpendicular to all of the field lines an equipotential line (meaning they have the same electric potential), and no energy difference will be found between them. With out an energy gradient, there will be no horizontal detection( or movement).
A positively charged plate and a negatively charged plate are separated by a distance d as shown below. Which of the following correctly depicts the electric field lines between these two plates? (See picture #97) A. see picture 98 B. See picture 99 C. See picture 100 D. There would be no net electric field between the plates
A. This correctly deducts the direction in which a positive test charge would be compelled to move when placed between two oppositely charged plates. Field lines are used to represent the electrical field vectors for a charge. By convection, they point in the direction that a positive test charge would move in the presence of the electrical charges. Therefore they point away from the positive charge and towards the negative charge. Field lines never cross each other.
(See picture #101) At what point in the circuit does an electron have the greatest electric potential energy? A. when leaving the battery B. when entering the cathode ray tube C. When passing between the deflector plates D. When exiting the cathode ray
A. The electrons have the greatest electric potential energy
When one sodium cation is transferred by the Na+/K+ ATPase from the intracellular space to the extracellular space, what is its change in electric potential energy if the membrane potential is -70mV? (The charge of an electron is approximately 1.602 x 10^-19C) A. -1.12 x 10^-20J B. 1.12 x 10^-20J C. -8.92 x 10^-19J D. 8.92 x 10^-19J
B. Use the equation U = (delta V) x q It is standard, when speaking of membrane potential, to use the extracellular space as a reference, so a membrane potential of -70mV implies that the inside of the cell is more negative then the outside. Since a positive ion is moving from a negative environment to a more positive one, its potential energy must be increasing. We then plug our numbers into the equation and get (70 x 10^-3)(1.602 x 10^19C) = 1.12 x 10^-20 J
A particular nerve cell membrane has a resting membrane potential of -70 mV. A sodium ion a short distance from the membrane feels an electron force, F, causing net movement of the sodium ion toward the membrane. What is the magnitude of the electron force when the sodium ion is at half its original distance? A. F/2 B. F C. 2F D. 4F
D. Applying Coulomb's law to determine the magnitude of the force: Fe = (kq1q2)/r^2 = (1/2r)^2 = 1/4r^2 which turns into 4 since the 1/4 is on the bottom
The electric field a distance d from an ATP molecule has a magnitude of 81 N/C. At what distance from the ATP molecule will the magnitude of the electric field equal 1 N/C? A. d/9 B. d/3 C. 3d D. 9d
D. The magnitude of the electric field is inversely proportional to the square of the distance from the source charge. Take the ratio of initial and final electric fields and solve for for d.