Chapter 5 charged particles

Question 1

What is an electric field?

Answer 1

A region of space around a charged object where another charged object experiences a force.

Question 2

How are electric field lines drawn?

Answer 2

They point away from positive charges and towards negative charges. The density of lines shows the field’s strength.

think “what direction would a test positive charge go”

Question 3

What is the equation for force on a charge in an electric field?

Answer 3

F = qE,
where
F = force (N),
q = charge (C),
E = field strength (N/C).

Question 4

How is acceleration of a charged particle in an electric field found?

Answer 4

Use F = qE and Newton’s 2nd law
(F = ma).
Therefore, a = qE / m.

Question 5

What is the equation for electric field strength between parallel plates?

Answer 5

E = V / d,
where
V = potential difference (V)
d = separation (m).

Question 6

What is the equation for work done moving a charge in an electric field?

Answer 6

W = qV or W = qEd,
where
W = work (J),
q = charge (C),
V = potential difference (V),
E = field strength (N/C),
d = distance (m).

Question 7

What does work done by an electric field represent?

Answer 7

The change in electrical potential energy of the charge.

Question 8

How is projectile motion of a charge in an electric field similar to gravity?

Answer 8

Both** produce constant acceleration**, giving a parabolic path when combined with horizontal velocity.

Question 9

What is the ‘electron-gun’ equation?

Answer 9

½mv² = qV,
v= √(2qV/m)
relating kinetic energy gained by a charge to potential difference.

Question 10

What is the force on a moving charge in a magnetic field?

Answer 10

F = qvB sinθ,
where
q = charge (C),
v = velocity (m/s),
B = field strength (T),
θ = angle between v and B.

Question 11

When is the magnetic force on a moving charge maximum?

Answer 11

When velocity is perpendicular to the field (θ = 90°).

Question 12

When is the magnetic force zero?

Answer 12

When velocity is parallel to the magnetic field (θ = 0° or 180°).

or the particle is not moving ie v=0

Question 13

How do you determine force direction on a positive charge in a magnetic field?

Answer 13

Use the right-hand rule: thumb = velocity, fingers = magnetic field, palm = force direction.

thumb points to direction of positive charge (or convential current).** need to reverse the thumb direction** wwhen dealing with electrons

Question 14

How do you determine force direction on a negative charge in a magnetic field?

Answer 14

Apply the right-hand rule for a positive charge, then reverse the direction of your thumb.

Question 15

What is the equation for radius of a circular path of a charged particle in a magnetic field?

Answer 15

**r = mv / qB, **
where
m = mass,
v = speed,
q = charge,
B = magnetic field.

centripedal force = force in magnetic field

Question 16

Why do charged particles move in circles in a magnetic field?

Answer 16

The magnetic force acts as a centripetal force, always perpendicular to velocity.

which is the definition of circular motion

Question 17

How can synchrotrons bend high-speed particles into circular paths?

Answer 17

Strong magnetic fields provide the centripetal force, allowing acceleration over long paths without straight tunnels.

Question 18

What practical technologies use charged particle deflection?

Answer 18

Cathode ray tubes (CRTs), mass spectrometers, particle accelerators.

Question 19

Compare electric and magnetic field forces on charges.

Answer 19

Electric fields accelerate charges along or against the field;
magnetic fields deflect charges at right angles without changing speed.