Download Electrical Force - Scarsdale Schools

Superposition of Forces
• Two point charges are located on the x axis of
a coordinate system: q1 = -1 nC and is at
= -2.0 cm; q2 = -3 nC and is at = 4.0 cm.
What is the total electric force exerted by q1
and q2 on q3 = 5.0 nC at the origin?
Fields
• A point charge q = -8.0 nC is located at the
origin. Find the electrical field at the field
point x = 1.2 m and y = -1.6 m
Different But the Same
• A positron (the electron’s antiparticle) has
mass 9.1 x 10^-31 kg and charge q = 1.6 x
10^-19 C. Suppose a positron moves in the
vicinity of an (alpha) particle, which has
charge 3.2 x 10^-19 C. The alpha particle’s
mass is more than 7000 times that of the
positron, so we assume that the particle
remains at rest.
Continued
• When the positron is 1 x 10^-11 m from the
particle, it is moving directly away from the
particle at 3 x 10^6 m/s. (a) What is the
positron’s speed when the particles are
2 x 10^-10 m apart? (b) What is the positron’s
speed when it is very far from the particle?
Realize Your Potential
(a) An electron is to be accelerated from
3 x 106 m/s to 6 x 106 m/s. Through what
potential difference must the electron pass to
accomplish this?
(b) Through what potential difference must the
electron pass if it is to be slowed from to a
halt?
Tube TVs…
• An electron with an initial speed of
6.5 x 106 m/s is projected along the axis
midway between the deflection plates of a
cathode-ray tube. The potential difference
between the two plates is 22 V and the top
plate possesses positive charge. (a) What is
the force on the electron when it is between the
plates?
And…
How They Work
• (b) What is the acceleration of the electron when
acted on by the force in part (a)?
• (c) How far above the axis has the electron moved
when it reaches the end of the plates
• (d) At what angle with the axis is it moving as it
leaves the plates?
• (e) How far above the axis will the electron strike
the fluorescent screen S?
What Ya Think?
• If you double the amount of charge on a
parallel pate capacitor, what happens to its
capacitance? (i) It increases; (ii) it decreases;
(iii) it remains the same; (iv) the answer
depends on the size or shape of the conductors
Plates
• The plates of a parallel-plate capacitor in
vacuum are 5.00 mm apart and 2.00 m2 in area.
A 10.0-kV potential difference is applied
across the capacitor. Compute (a) the
capacitance; (b) the charge on each plate; and
(c) the magnitude of the electric field between
the plates