Electrons are emitted from a conductor when the conductor is:

Question

A. Exposed to weak light
B. cooled rapidly
c.bombarded by high-speed electrons
d.subjected to a small voltage

Answer 1

c. Photomultiplier tube light detectors use this principle.
See
http://quarknet.fnal.gov/projects/pmt/student/dynodes.shtml
for a discussion

The process is called secondary emission.