Discovery Of The Electron - William Crookes Flashcards
What did William Crookes discover?
Cathode rays
Who discovered cathode rays?
William Crookes
What experiment did Crookes carry out first?
He carried out an experiment to investigate what happens when an electric current is passed through a glass tube containing air at low pressure
What is the glass used by Crookes commonly called?
A vacuum tube
When carrying out his experiment, what did Crookes find?
He found that radiation was coming from the metal plate inside the tube connected to the negative end of the power supply
Describe the apparatus used by Crooks in his first experiment
(4)
A vacuum tube containing a Maltese cross
The Maltese cross found in the middle of the tube is connected to the positive end of a power supply (anode)
A metal plate at the small end of the vacuum tube is connected to the negative end of the power source (cathode)
Shadow of the Maltese cross appears on the opposite side of the vacuum tube to the cathode
What is the negative plate inside the vacuum tube called?
The cathode
What is the positive cross inside the vacuum tube called?
The anode
What was formed at the other end of the tube from the cathode?
A shadow of the Maltese cross
What is placed in the middle of the vacuum tube?
A Maltese cross
What name did Crookes use to describe the rays coming from the cathode?
Cathode rays
What happens when the cathode rays strike the glass?
The cathode rays themselves are invisible but they cause the glass to glow or fluoresce
What causes the shadow?
The cathode rays being stopped by the Maltese cross
Why did Crookes carry out a second experiment?
To investigate the properties of cathode rays
Describe Crookes’ second experiment
He placed a light paddle wheel, mounted on rails in front of the cathode
What did Crookes discover when the current was switched on during his second experiment?
He found that the paddle wheel rotated and travelled down the tube
During his second experiment. what did Crookes put in front of the cathode?
He put a light paddle wheel, mounted on rails in front
During his second experiment, what did Crookes mount the light paddle wheel on?
On rails
During his second experiment, what did Crookes notice when the paddle wheel began to spin?
He noticed that the vanes always turned away from the cathode
What did Crookes conclude from his second experiment?
He concluded that the vanes were being struck by particles coming from the cathode
What three deductions did Crookes make from his two experiments?
(3)
Cathode rays travel in straight lines (shadow of cross was sharp)
Cathode rays cause glass to fluoresce when they strike it
Cathode rays posses enough energy to move a paddle wheel
Why could Crookes deduct that the cathode rays travelled in a straight line?
Because the shadow of the Maltese cross was sharp
What do cathode rays cause to fluoresce?
Glass
How much energy do cathode rays have?
Enough to move a paddle wheel
