# Cathode Ray Tube Magnetic Question

• science.girl
In summary, the conversation discusses a cross section of a cathode ray tube and the movement of an electron through a magnetic field. The direction and magnitude of the magnetic force on the electron is determined, as well as the radius of curvature of its path. Later, an electric field is introduced to cancel out the magnetic deflection of the electron. The direction and magnitude of the electric field are also discussed.
science.girl

## Homework Statement

The figure from the link below shows a cross section of a cathode ray tube. An electron in the tube initially moves horizontally in the plane of the cross section at a speed of 2.0 x 107 meters per second. The electron is deflected upward by a magnetic field that has a field strength of 6.0 x 10-4 tesla.
a. What is the direction of the magnetic field?
b. Determine the magnitude of the magnetic force acting on the electron.
c. Determine the radius of curvature of the path followed by the electron while it is in the magnetic field.

An electric field is later established in the same region as the magnetic field such that the electron now passes through the magnetic and electric fields without deflection.
d. Determine the magnitude of the electric field.
e. What is the direction of the electric field?

I found the picture at this link on page 6: harmonphys.info/magnetism%20problems.doc

## Homework Equations

F = qvBsin$$\theta$$

r = (mv)/(qB)

## The Attempt at a Solution

a) It is directed out of the page by the right hand rule. (Did I do this properly?)

b) F = qvBsin$$\theta$$
F = (1.60*10^(-19) C)(2.0*10^7 m/s)(6.0*10^(-4))sin$$\theta$$

How do I determine $$\theta$$?

c) r = (mv)/(qB)
r = [(9.11*10^(-31) kg)(2.0*10^7 m/s)] / [(1.60*10^(-19) C)(6.0*10^(-4) T)
r = .1898 m

d) Would the electrical and magnetic fields cancel? How do I set this up?
e) Would this be the opposite of (a)? [i.e., into the page?]

## Homework Equations

F = qvBsin$$\theta$$

r = (mv)/(qB)

## The Attempt at a Solution

a) It is directed out of the page by the right hand rule. (Did I do this properly?)

b) F = qvBsin$$\theta$$
F = (1.60*10^(-19) C)(2.0*10^7 m/s)(6.0*10^(-4))sin$$\theta$$

How do I determine $$\theta$$?

v and B are perpendicular. Therefore θ is 90 degrees.

c) r = (mv)/(qB)
r = [(9.11*10^(-31) kg)(2.0*10^7 m/s)] / [(1.60*10^(-19) C)(6.0*10^(-4) T)
r = .1898 m

d) Would the electrical and magnetic fields cancel? How do I set this up?
e) Would this be the opposite of (a)? [i.e., into the page?][/QUOTE]

Due to magnetic field B, the centripetal force mv^2/r bends the electron beam in the upward direction. To nullify this deflection an electric force Eq should act in the downward direction.

Thank you, rl.bhat!

## 1. What is a cathode ray tube?

A cathode ray tube (CRT) is a vacuum tube that uses an electron gun to project a beam of electrons onto a phosphorescent screen, creating images on a television or computer monitor.

## 2. How does a cathode ray tube work?

A cathode ray tube works by using an electron gun to fire a beam of electrons towards a phosphorescent screen. The screen is coated with red, green, and blue phosphors which light up when struck by the electrons, creating the image seen on the screen. The beam of electrons is controlled by electromagnetic fields generated by the deflection coils.

## 3. What is the purpose of the magnetic question in the cathode ray tube?

The magnetic question, also known as the magnetic focusing question, is used to control the focus of the electron beam in a cathode ray tube. By manipulating the magnetic fields, the beam can be focused onto a specific point on the screen, creating a clear image.

## 4. What are the advantages of using a cathode ray tube in displays?

Cathode ray tubes have several advantages, including the ability to produce high-quality images with good color accuracy, a wide viewing angle, and fast response times. They are also relatively inexpensive to produce and have a long lifespan.

## 5. What are the potential health hazards associated with cathode ray tubes?

Cathode ray tubes emit low levels of radiation, which can be harmful if someone is exposed to it for extended periods of time. Additionally, the glass screen can break and release harmful substances if not disposed of properly. However, modern CRTs have safety features in place to minimize these risks and proper disposal methods are available.

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