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• # Difficult Problems in Physics From Jamb 2004

Physics

05-02-2016 13:14:00 +0000

Some 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

• Opeyemi tunde

d

0 05-02-2016 18:15:00 +0000

• Collins Nwanneka

40=B

0 05-02-2016 18:19:00 +0000

• nena Ogbonnaya

40-D, 41-A

0 05-02-2016 18:20:00 +0000

• Chimezie Victor

0 05-02-2016 18:26:00 +0000

• Az Ultimate

40 C

0 05-02-2016 18:42:00 +0000

• Shobande Daniel

electrophorous

0 05-02-2016 20:17:00 +0000

• Shobande Daniel

a....7.6

0 05-02-2016 20:23:00 +0000

• OAA Oke

que 41-c

0 06-02-2016 07:59:00 +0000

• Catherine Akpan