I have to do a lab on cathode ray tubes. Can you explain to me how the cathode ray tubes work? And can you mention the voltages involved, what they do, and what effect varying these voltages has on the electron beam.

I suggest you start here:

http://electronics.howstuffworks.com/tv3.htm

There are several pages that you will have to access one at a time by clicking at the bottom of each page.

For about 60 years, cathode ray tubes were what you looked at when watching TV or a computer monitor. They are still used for oscilloscopes and many other visual display devices. They are becoming obsolete as more efficient high-resolution visual display devices such as liquid crystal screens have been developed.

Of course! Cathode ray tubes (CRTs) are vacuum tubes that produce a beam of electrons, also known as a cathode ray, which can be manipulated to create images on a screen. Here's an overview of how CRTs work:

1. Electron Gun: The CRT contains an electron gun, consisting of a cathode and one or more control grids. The cathode emits electrons through a process called thermionic emission when it's heated. The control grids help to focus and accelerate the electron beam.

2. Acceleration: To accelerate the electron beam, a high voltage, typically several thousand volts, is applied between the cathode and an anode, creating a strong electric field. This voltage is called the accelerating voltage. The electric field accelerates the electrons towards the screen at a high velocity.

3. Deflection: The electron beam is then deflected using electromagnetic fields generated by deflection coils. There are two sets of coils—horizontal and vertical deflection coils—that can independently adjust the position of the beam on the screen. By varying the current passing through these coils, the beam can be moved in any direction, allowing the creation of images.

Varying the voltages in a CRT can have several effects on the electron beam:

1. Accelerating Voltage: Increasing the accelerating voltage speeds up the electrons, resulting in a more energetic electron beam. This leads to brighter phosphor illumination and a higher contrast image. However, excessively high voltages can result in excessive heat generation and may lead to damaging the CRT.

2. Focus Voltage: Adjusting the focus voltage allows for the fine-tuning of the electron beam's focus. Lower voltages can result in a broader beam, causing a blurrier image. Raising the focus voltage tightens the beam, leading to sharper image lines.

3. Deflection Voltage: Changing the voltages applied to the deflection coils controls the position of the electron beam on the screen. Manipulating the deflection voltages allows the scanning of the beam across the entire screen, creating different images or moving the electron beam in real-time applications like televisions.

It's important to note that specific voltage values and their effects can differ between different CRT models and designs. Therefore, it's essential to refer to the manufacturer's specifications or lab instructions for specific voltage values and their corresponding effects.