NEPAL ENGINEERING SERVICES

Friday, May 24, 2019

IOE Entrance Physics Part I: Capacitor.

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Every conductor has capacity to store charges, and the conductor that stores both positive and negative charges is called capacitor. It is also called condenser.


Capacitance=(Magnitude of charge on plate/Potential difference between the plates)
C=(Q/V)


Parallel Plate Capacitors:
Parallel plate capacitors are a type of capacitors which have two plates(electrodes) and dielectric(insulating material). The two plates are equal in size and parallel to each other with certain gap filled with dielectric. 

Electric field between parallel plate capacitors 
=  (σ/2εo)+(σ/εo)

Capacitance

=(εoA/d)
=(
εoA/(d-t(1-1/k)))

Spherical Capacitor(Concentric Spheres):
C=4
πεokab/(a-b)

For single Sphere:

C=4πεoa

Combination of Capacitors:

1) Series Capacitors:
Q1=Q2=Q3=Q4
V=V1+V2+V3
(1/C)=(1/C1)+(1/C2)+(1/C3)
  •  Charge remains same in all capacitors.
  • Potential difference is different in each capacitor.

 2) Parallel Capacitors:

Q=Q1+Q2+Q3+Q4
V1=V2=V3=V4
C=C1+C2+C3+C4

  • Charge is different in each capacitor
  • Potential difference is same in each capacitor.
Energy Stored in Capacitor:
U=CV²/2
  = Q
²/2C
  = QV/2

Energy Density: E=V/d

Cylindrical Capacitor:
C = \dfrac{2 \pi \epsilon_0 \epsilon_r L }{\log_e \left( \dfrac{R_2}{R_1}\right)} F


Some questions asked in IOE entrance exams are:

  In a 20 Vac series RC circuit, if 20 V is measured across the resistor and 40 V is measured across the capacitor, the applied voltage is:
a. 45V b. 50 V c. 55V d. 60V

 Capacitor is a device used to__________
a) store electrical energy
b) vary the resistance
c) store magnetic energy
d) dissipate energy

 Capacitor stores which type of energy?
a) kinetic energy
b) vibrational energy
c) potential energy
d) heat energy

Which of the following is a passive device?
a) Transistor
b) Rectifier
c) Capacitor
d) Vaccuum Tubes



For which medium capacitance is high?
a) Air
b) Mica
c) Water
d) Metal


Van de Graaf generator is used to
(a) measure high potential difference
(b) produce high DC potential
(c) produce high AC potential
(d) compare high DC potential
 

 The unit of electric field strength is
(a) Newton/Coulomb
(b) Volt/meter
(c)Joule/Coulomb x meter
(d) all of above

 Two identical capacitors are joined in parallel, charged to potential V, separated and then connected in series i.e. the positive plate of one is connectei to the negative plate of other
(a) the charge on the free plates connected together are destroyed
(b) charges on the free plates are enhanced
(c) the energy stored in the system increases
(d) the potential difference between the free plates is 2 V

In order to increase the capacity of a parallel- plate condenser one should , introduce between the plates a sheet of 、
(a)Tin
(b) copper 
(c) mica
(d) steel 2,

To a given capacitor another is connected in parallel to
(a) increase the capacitance
(b)decrease the capacitance
(c) increase its active life
(d) improve performance

For more Topics on IOE entrance exam you may visit:
Institute of Engineering (IOE) Nepal Entrance exam (BE and BArch): Exam leading you to the path of being an engineer and architecture.

IOE entrance Aptitude Test: Part I (Isometric figures)

IOE entrance Aptitude Test: Part II (Input devices, Output devices and Operating System)

IOE entrance Aptitude Test: Part III: Traffic Signals, Signs, Number system, Storage units, Renewable energy, Non-renewable energy

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