1. 5.5 Electric Field and Voltage – Uniform Field p. 200 Electric Field and Voltage – Uniform Field A small test charge will experience a constant force anywhere between two charge plates due to the uniform electric field found there. V = EpEp Q Fd Q = F Q =d F Q E = EdV = V d E = Remembering the definition of Voltage: And: Electric field strength between two charged plates: Therefore: {units: V/m = N/C}

2. 5.5 Electric Field and Voltage – Uniform Field Application of Uniform Electric Fields – The Cathode Ray Tube p. 203 A cathode ray tube (CRT) is a special vacuum tube that creates a focused beam of electrons. Used in old fashioned TV sets, monitors and oscilloscopes. The CRT has two key parts: 1)Accelerating anode to generate a focused beam of electrons 2)Deflecting plates to move the beam of electrons to various places on the screen.

3. 5.5 Electric Field and Voltage – Uniform Field How the beam Is Focused an accelerated p. 203 Once the electrons are generated by the heating filament in a CRT, they are accelerated by an accelerating anode, which is essentially a charged plate with a high voltage (500 V – 1000 V in a classroom model). The potential energy of the electrons in an uniform electric field causes the electrons to increase speeds as they move across the uniform electric field. V a = EpEp Q EkEk Q = 1/2mv 2 Q = Where:V a = accelerating voltage (V) m = mass of electron = 9.11 x 10 -31 kg v = maximum speed of electrons (m/s) Q = charge on electron = 1.6 x 10 -19 C Therefore: v is proportional to the V a !

4. 5.5 Electric Field and Voltage – Uniform Field How Does the amount of Deflection Depend on Electric Field? p. 205 Once the accelerating plates make the electrons travel at a high speed the deflecting plates are used to deflect or position the beam of electrons at some point of the screen of the CRT. y = 1/2at 2 Deflection of beam while in between the deflecting plates: F m a = Newton’s 2 nd Law: y = 1Ft 2 2m And: F = EQy = 1EQt 2 2m And: For a particular CRT and at a certain accelerating voltage, ½, Q, m, and t will remain constant, which means: y α V d The deflection, y, inside the deflecting plates is proportional to the deflecting voltage V d.

5. 5.5 Electric Field and Voltage – Uniform Field How Does the Amount of Deflection Depend on E? p. 205 The time for the electron beam to travel distance x, from deflecting plates to the screen: t = x/v x. The beam is deflected by the deflecting plates and follows a curved path while between the deflecting plates. Once the beam of electrons leave the deflecting plates, the beam will follow a straight line until it reaches the screen. The amount of deflection on the screen is directly proportional to the amount of deflection inside the deflecting plates. Therefore the deflection you see on the screen, y ' is directly proportional to δ (deflection between deflecting plates) and : y ' α V d

6. 5.5 Electric Field and Voltage – Uniform Field How the deflection, y ' on the screen of a CRT depends on accelerating voltage (V a ) and deflecting voltage V d. p. 205 VaVa VdVd y'y' The higher the accelerating voltage the faster the electrons travel and therefore the less time t the deflecting voltage will be able to deflect them. Higher V a means less deflection, y '. On the other hand, the higher the deflecting voltage the stronger the force on the electrons, moving the electrons further off their straight line path. Higher the V d the greater the deflection y ' y' αy' α VdVd VaVa Summing it up:

7. 5.5 Electric Field and Voltage – Uniform Field Key Questions In this section, you should understand how to solve the following key questions. Page 202 – Practice Problem 5.5.1: #2 Page 207 – Quick Check #1 - 3 Page 211 - 213 – Review 5.5 #2,3,5,7, & 11