Electrons are emitted from a conductor when the conductor is
A. subjected to a small voltage.
B. exposed to weak light.
C. bombarded by high-speed electrons.
D. cooled rapidly.
bombarded by high-speed electrons.
C. Bombarded by high-speed electrons
The correct answer is C. bombarded by high-speed electrons.
Electrons are emitted from a conductor through a process known as the "photoelectric effect." This effect occurs when high-speed electrons collide with the atoms of the conductor, knocking out some electrons from their original positions. These emitted electrons are called "photoelectrons."
To determine which option is correct, we need to consider the conditions necessary for the photoelectric effect to occur.
Option A states that electrons are emitted when the conductor is subjected to a small voltage. While applying a voltage to a conductor can create an electric field, it does not guarantee the emission of electrons. Therefore, this option is incorrect.
Option B suggests that electrons are emitted from a conductor when exposed to weak light. This is partly correct. Normally, the photoelectric effect requires the conductor to be exposed to a sufficiently high frequency or energetic light (such as ultraviolet or X-ray radiation) rather than weak light. Therefore, this option is not fully accurate.
Option C claims that electrons are emitted from a conductor when bombarded by high-speed electrons. This option is correct. When high-speed electrons collide with a conductor, they can transfer enough energy to dislodge electrons from their orbits within the atoms of the conductor. This collision-induced emission of electrons is the principle behind devices such as electron guns and electron microscopes.
Option D suggests that cooling the conductor rapidly causes electron emission. Cooling can certainly have effects on the behavior of electrons in a material but does not directly lead to their emission. Therefore, this option is incorrect.
In conclusion, the correct answer is C. Electrons are emitted from a conductor when the conductor is bombarded by high-speed electrons.