What is the longest wavelength that will cause photoemission of electrons from the following tungsten-coated cathodes: W-Th, W-Ba, and W-Cs? A cable consists of three strands of copper wire each 1 m...

What is the longest wavelength that will cause photoemission of electrons from the following tungsten-coated cathodes: W-Th, W-Ba, and W-Cs?

A cable consists of three strands of copper wire each 1 m long and 250 /itm in diameter. What is the room-temperature resistance of the cable?