Electrical Transformers and Rotating Machines
4th Edition
ISBN: 9781305494817
Author: Stephen L. Herman
Publisher: Cengage Learning
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Textbook Question
Chapter 1, Problem 1RQ
Is the north magnetic pole of the earth a north polarity or a south polarity?
Expert Solution & Answer
To determine
Whether the north magnetic pole of earth is of north polarity or south polarity.
Explanation of Solution
The phenomenon of interchanging of the magnetic north pole and magnetic south pole is termed as geomagnetic reversal. These reversal occurrences are statically random in nature. The Earth is surrounded entirely by magnetic lines of forces. It can also be said that it is surrounded by a magnetic shell. Due of the fact, that unlike magnetic poles attract each other, the south magnetic pole of the Earth attracts the north magnetic pole of the compass needle.
Thus, the north magnetic pole of earth is actually of south polarity.
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2 A metal block of mass m = 10 kg is sliding along a frictionless surface with an initial speed
Vo, as indicated below. The block then slides above an electromagnetic brake that applies a
force FEB to the block, opposing its motion. The magnitude of the electromagnetic force
varies quadratically with the distance moved along the brake (x):
10
FEB = kx²,
with k
= 5
N
m²
V₁ = 8 m/s
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FEB
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Q1: Determine the length, angle of contact, and width of a 9.75 mm thick
leather belt required to transmit 15 kW from a motor running at 900 r.p.m. The
diameter of the driving pulley of the motor is 300 mm. The driven pulley runs at
300 r.p.m. and the distance between the centers of two pulleys is 3 meters. The
density of the leather is 1000 kg/m³. The maximum allowable stress in the
leather is 2.5 MPa. The coefficient of friction between the leather and pulley is
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5. A 15 kW and 1200 r.p.m. motor drives a compressor at 300 r.p.m. through a pair of spur gears having
20° stub teeth. The centre to centre distance between the shafts is 400 mm. The motor pinion is made
of forged steel having an allowable static stress as 210 MPa, while the gear is made of cast steel
having allowable static stress as 140 MPa. Assuming that the drive operates 8 to 10 hours per day
under light shock conditions, find from the standpoint of strength,
1. Module; 2. Face width and 3. Number of teeth and pitch circle diameter of each gear.
Check the gears thus designed from the consideration of wear. The surface endurance limit may be
taken as 700 MPa. [Ans. m = 6 mm; b= 60 mm; Tp=24; T=96; Dp = 144mm; DG = 576 mm]
Chapter 1 Solutions
Electrical Transformers and Rotating Machines
Ch. 1 - Is the north magnetic pole of the earth a north...Ch. 1 - What were early natural magnets known as?
Ch. 1 - The south pole of one magnet is brought close to...Ch. 1 - How can the polarity of an electromagnet be...Ch. 1 - Define the following terms:
Flux...Ch. 1 - A force of 1 ounce is equal to how many dynes?
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