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A coil is wound with 300 turns over a stee ring of relative permeability 900 having a mean circumference of 400 mm and a cross-sectional area of 500 mm2 . If the coil has a resistance of 8Ω and is connected across a 20V dc supply, using a neat sketch, calculate:
a).The coil magneto-motive force
b).The magnetic field strength
c).The total flux
d).The reluctance of the ring
e).The permeance of the ring and
f).The flux density in the ring
A sling Psychrometer reads, 40°c dry bulb
Temprature and 28 degree Celsius Wet bulb temp. Calculate:
(1)Specific humidity
(2) Relative humidity
(3) Vapour density
(4)Dew point temperature
(5) specific Enthalpy.
The equation for the instantaneous voltage across a
discharging capacitor is given by v = Voe
-l-
, where Vo is
the initial voltage and r is the time constant of the circuit.
The tasks are to:
a)
b)
C)
Draw a graph of voltage against time for Vo=12V
and r = 2s, between t = Os and t = 10s.
Calculate the gradient at t = 2s and t = 4s.
Differentiate v = 12e 2 and calculate the value of
du
dt
at t= 2s and t= 4s.
d)
e)
Compare your answers for part b and part c.
Calculate the second derivative of the instantaneous
¿2.
di2
3).
Differentiate the equation to find the functions for
ds
i)
Velocity
dt
ii) Acceleration
(a
83
=
dt?
d) Use your result from part c to calculate the velocity at
A 162-MHz carrier is deviated by 12 KHz by a 2-KHz modulating signal. What is the modulation index?
n a four-bar chain ABCD, AD is fixed link 0.12 m long, crank AB is 0.03 m long and
rotates uniformly at 100 rpm clockwise while the crank CD is 0.06 m long and rotates
about D. Link BC is equal to link AD. Find the angular velocity of link DC when angle
BAD is 600
.
A block weighing 60 N rests on a horizontal floor. a) What is the minimum force that will make the block move if the coefficient of static friction is 0.20? b) What is the minimum force that will keep the block moving at uniform speed once it starts moving if the coefficient of kinetic friction is 0.10?
A 0.8 m high, 1.5 m wide double pane window consists of two 4 mm
thick layers of glass (k=78 W/mK) and is separated by a 10 mm wide
stagnant air space (k=0.026W/mK). The room is at 20°C and the
outside air is at -10°C. The heat transfer coefficients are 10 and 40
W/m2K. find
i) The rate if heat transfer through the window
ii) The inside surface temperature
An 8-ohm resistor is in series with an inductive coil and the combination is connected
across a 120 V, 60 Hz source. A voltmeter connected across the resistor reads 32 V and 104 when connected across the coil. Determine the resistance of the coil.
The ohmic resistance of a large magnetic contractor is measured to be 20 ohms. A 230 V is
impressed on the contractor and the current is taken as 3.2 A. Neglecting core loss, determine
the inductance of the contractor in mH?
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