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Difficult Problems in Physics From Jamb 2004
Physics
Admin Admin
05-02-2016 13:14:00 +0000Some more questions that 80% of the people that attempted it failed. See it you can get it right.
(Question 40) The instrument used for securing a large number of similar charges by induction is called
A. Capacitor
B. Electrophorus
C. Electroscope
D. Proof-plane
(Question 41) A steady current 2A flows in a coil of e.m.f. 12V for 0.4s. A back e.m.f. of 3V was induced during this period. The stored energy in the loop that can be utilized is
A. 7.2J
B. 1.2J
C. 2.4J
D. 9.6J
UPDATED - ANSWERS ON QUESTIONS ABOVE
Question 40
SOLUTION
B - Electrophorus
EXPLANATION
Electrophorus is a device use to generate or produce or secure a large number of similar charge by the process of electrostatic induction
Capacitor is a device use to store charge
Electroscope is a device use to test the polarity and magnitude of electrostatic charge e.g is the gold leaf electroscope.
Proof plane is an aluminium covered disk conductor attached to an insulated handle used to transfer charges.
Question 41
SOLUTION
B 1.2J
EXPLANATION
back emf = 3v
time = 0.4s
current = 2A
Recall that the energy stored in an inductor is given by
Energy store = average power × time E = 1/2VI ×t
where V = back emf = 3v, I = 2A, time t = 0.4s then Energy E = 1/2(back emf x time x current)
E = 1/2 × 3 x 0.4 x 2
= 1.2j
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