A) lithium and beryllium
Explanation:
From the given row on the periodic table, only lithium and beryllium will conduct electricity.
What makes a substance able to conduct electricity?
- The presence of free mobile electrons and in some, ions allows them to carry electric currents.
Metals are generally known to be good conductors of heat and electricity. This is because, metals have a large pool of electrons i.e free mobile electrons. They are electropositive with a large size and readily release their electrons for conduction.
Lithium and Beryllium are in the metallic block on the periodic table.
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Answer:
The photoelectric effect occurs only for frequencies above the cutoff frequency, regardless of the intensity.
Explanation:
The photoelectric effect occurs when light is shined on metals such as zinc beyond a certain frequency (the threshold frequency), which causes electrons to escape from the zinc. The electrons which are fleeing are called photo electrons.
Therefore photo electric effect is
The photoelectric effect occurs only for frequencies above the cutoff frequency, regardless of the intensity.
Answer:
Time required by boat 1 for the round trip is less than that of boat 2.
Hence, boat 1 wins.
Explanation:
Case 1: Boat 1
Speed of boat = 
time = 
While going to another end
time =
time = 
time = 1 hour
While going back,
time =
time =
time = 1 hour
Total time taken by boat 1 is,
Total time by boat 1 = 1 hour + 1 hour = 2 hour
Total time by boat 1 = 2 hour
Total time taken by boat 1 for the round trip is 2 hour.
Case 2: Boat 2
Speed of boat =
time =
While going to another end
time =
time = 
time = 2 hour
While going back,
time =
time = 
time = 0.66 hour
Total time taken by boat 2 is,
Total time by boat 1 = 2 hour + 0.66 hour
Total time by boat 1 = 2.66 hour
Total time taken by boat 2 for the round trip is 2.66 hour.
Time required by boat 1 for the round trip is less than that of boat 2.
Hence, boat 1 wins.
