When electrical power is transmitted over long distances, the voltage is stepped up so that
the resistance of the wire may be increased proportionately to the potential difference
the time of transmissions between the generating and the receiving stations may be reduced
there is increased current to produce brighter lights.
the rate of electrical consumption is increased.
the energy waste may be minimised as the current is lowered.
Correct answer is E
No explanation has been provided for this answer.
Which of the following is used in a nuclear reactor to slow down fast moving neutrons?
graphite rods
carbon dioxide gas
liquid sodium metal
concrete shield
boron rods
Correct answer is A
No explanation has been provided for this answer.
The half-life of a radioactive substance is 2 seconds. Calculate the decay constant.
2.890 s-1
1.445 s-1
0.576 s-1
0.347s-1
0.152 s-1
Correct answer is D
\(T_{\frac{1}{2}} = \frac{\ln 2}{\lambda}\)
where \(T_{\frac{1}{2}}\) = half-life of element; \(\lambda\) = decay constant.
= \(\frac{0.693}{\lambda}\)
\(\therefore 2 = \frac{0.693}{\lambda}\)
\(\lambda = \frac{0.693}{2}\)
= 0.3465 s\(^{-1}\)
\(\approxeq\) 0.347 s\(^{-1}\)
photoelectric effect
thermionic emission
field emission
secondary emission
radioactive emission
Correct answer is B
The process by which free electrons are emitted from the surface of a metal when external heat energy is applied is called thermionic emission.
has three pro tons and two neutrons
has two protons and one neutron
has two protons and three neutrons
has one proton and two neutrons
cannot exist because it has the same mass number as tritium
Correct answer is E
No explanation has been provided for this answer.