Physics
Physics
5th Edition
ISBN: 9781260486919
Author: GIAMBATTISTA
Publisher: MCG
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Chapter 20, Problem 34P

(a)

To determine

The current drawn by the motor when it is first started up.

(a)

Expert Solution
Check Mark

Answer to Problem 34P

The current drawn by the motor when it is first started up is 6.0A.

Explanation of Solution

Write an expression for the current drawn by the motor when it is first started up.

  I=εextR                                                                                                             (I)

Here, I  is the current drawn by the motor when it is first started up, εext is the external emf and R is the resistance.

Conclusion:

Substitute 12V for εext and 2.0Ω  for R in equation (I) to find I.

  I=12V2.0Ω=6.0A

Thus, the current drawn by the motor when it is first started up is 6.0A.

(b)

To determine

The current draws at normal operating speed.

(b)

Expert Solution
Check Mark

Answer to Problem 34P

The current draws at normal operating speed is 0.551A.

Explanation of Solution

Write an expression for Kirchhoff’s voltage law.

  εextI'Rεback=0                                                                                                (II)

Here, I'  is the current draw at normal operating speed and εback is the back emf.

Write an expression for back emf.

  εback=PI'                                                                                                     (III)

Here, P is the power.

Rewrite the expression (II) by using equation (III).

  εextI'RPI'=0I'εextI2RP=0                                                                                      (IV)

Rearrange (IV) to calculate I'.

  I'=εext±εext24(R)(P)2(R)                                                                   (V)

Conclusion:

Substitute 12V for εext, 2.0Ω for R and 6.0W for P in equation (V) to find I'.

  I'=12V±(12V)24(2.0Ω)(6.0W)2(2.0Ω)=12V±(12V)248V2(4.0Ω)=0.551A

Thus, the current draws at normal operating speed is 0.551A.

(c)

To determine

The back emf induced in the winding at normal speed.

(c)

Expert Solution
Check Mark

Answer to Problem 34P

The back emf induced in the winding at normal speed is 10.9V.

Explanation of Solution

Write an expression for back emf induced in the winding at normal speed.

  εback=εextIR                                                                                          (VI)

Here, εext is the back emf induced in the winding at normal speed.

Conclusion:

Substitute 12V for εext, 0.551A for I and 2.0Ω for R in equation (VI) to find εext.

  εback=12V(0.551A)(2.0Ω)=12V1.1V=10.9V

Thus, the back emf induced in the winding at normal speed 10.9V.

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Chapter 20 Solutions

Physics

Ch. 20.7 - Conceptual Practice Problem 20.8 Choosing a Core...Ch. 20.9 - CHECKPOINT 20.9 Five solenoids are wound with...Ch. 20.9 - Practice Problem 20.9 Power in an Inductor The...Ch. 20.10 - Prob. 20.10CPCh. 20.10 - Prob. 20.10PPCh. 20 - Prob. 1CQCh. 20 - Prob. 2CQCh. 20 - Prob. 3CQCh. 20 - Prob. 4CQCh. 20 - Prob. 5CQCh. 20 - Prob. 6CQCh. 20 - Prob. 7CQCh. 20 - Prob. 8CQCh. 20 - Prob. 9CQCh. 20 - Prob. 10CQCh. 20 - Prob. 11CQCh. 20 - Prob. 12CQCh. 20 - Prob. 13CQCh. 20 - Prob. 14CQCh. 20 - Prob. 15CQCh. 20 - Prob. 16CQCh. 20 - Prob. 17CQCh. 20 - Prob. 18CQCh. 20 - Prob. 19CQCh. 20 - Prob. 1MCQCh. 20 - Prob. 2MCQCh. 20 - Prob. 3MCQCh. 20 - Prob. 4MCQCh. 20 - Prob. 5MCQCh. 20 - Prob. 6MCQCh. 20 - Prob. 7MCQCh. 20 - Prob. 8MCQCh. 20 - Prob. 9MCQCh. 20 - Prob. 10MCQCh. 20 - A vertical metal rod of length 20 cm moves south...Ch. 20 - Suppose that the current were to flow in the...Ch. 20 - A vertical metal rod of length 36 cm moves north...Ch. 20 - Prob. 3PCh. 20 - Prob. 4PCh. 20 - Prob. 5PCh. 20 - Prob. 6PCh. 20 - In Fig. 20.2, a metal rod of length L is sliding...Ch. 20 - Prob. 9PCh. 20 - 4. In Fig. 20.2, what would the magnitude (in...Ch. 20 - Prob. 11PCh. 20 - 6. The armature of an ac generator is a circular...Ch. 20 - Prob. 13PCh. 20 - 8. A solid copper disk of radius R rotates at...Ch. 20 - 9. A horizontal desk surface measures 1.3 m × 1.0...Ch. 20 - The magnetic field between the poles of a magnet...Ch. 20 - Prob. 36PCh. 20 - 10. A square loop of wire, 0.75 m on each side,...Ch. 20 - 11. A long straight wire carrying a steady current...Ch. 20 - 12. A long straight wire carrying a current I is...Ch. 20 - Prob. 18PCh. 20 - 14. While I1 is increasing, what is the direction...Ch. 20 - 15. While I1 is constant, does current flow in...Ch. 20 - A circular conducting loop with radius 3.40 cm is...Ch. 20 - A circular conducting loop with radius 1.8 cm is...Ch. 20 - An external magnetic field parallel to the central...Ch. 20 - An external magnetic field is parallel to the...Ch. 20 - 19. In the figure, switch s is initially open. It...Ch. 20 - 20. Crocodiles are thought to be able to detect...Ch. 20 - 21. A bar magnet approaches a coil as shown, (a)...Ch. 20 - 22. Another example of motional emf is a rod...Ch. 20 - 23. Two loops of wire are next to each other in...Ch. 20 - 24. A dc motor has coils with a resistance of 16 Ω...Ch. 20 - Prob. 33PCh. 20 - Prob. 34PCh. 20 - Prob. 35PCh. 20 - 29. A doorbell uses a transformer to deliver an...Ch. 20 - Prob. 38PCh. 20 - 31. When the emf for the primary of a transformer...Ch. 20 - 32. A transformer with a primary coil of 1000...Ch. 20 - Prob. 41PCh. 20 - An ideal transformer takes an ac voltage of...Ch. 20 - 35. A 2 m long copper pipe is held vertically....Ch. 20 - In Problem 43, the pipe is suspended from a spring...Ch. 20 - Prob. 45PCh. 20 - Prob. 46PCh. 20 - 39. A solenoid of length 2.8 cm and diameter 0.75...Ch. 20 - Prob. 48PCh. 20 - Prob. 49PCh. 20 - Prob. 50PCh. 20 - Prob. 51PCh. 20 - 44. The current in a 0.080 H solenoid increases...Ch. 20 - Prob. 53PCh. 20 - Prob. 54PCh. 20 - Prob. 55PCh. 20 - Prob. 56PCh. 20 - Refer to Problem 56. After the switch has been...Ch. 20 - Prob. 59PCh. 20 - Prob. 61PCh. 20 - Prob. 58PCh. 20 - Prob. 60PCh. 20 - Prob. 63PCh. 20 - Prob. 62PCh. 20 - Prob. 64PCh. 20 - Prob. 65PCh. 20 - Prob. 66PCh. 20 - Prob. 68PCh. 20 - Prob. 67PCh. 20 - Prob. 70PCh. 20 - Prob. 69PCh. 20 - Prob. 72PCh. 20 - Prob. 71PCh. 20 - Prob. 74PCh. 20 - Prob. 73PCh. 20 - Prob. 75PCh. 20 - Prob. 76PCh. 20 - Prob. 77PCh. 20 - Prob. 78PCh. 20 - Prob. 79PCh. 20 - 72. A uniform magnetic field of magnitude 0.29 T...Ch. 20 - Prob. 81PCh. 20 - Prob. 82PCh. 20 - Prob. 83PCh. 20 - Prob. 85PCh. 20 - Prob. 84PCh. 20 - Prob. 86PCh. 20 - Prob. 87PCh. 20 - Prob. 88PCh. 20 - Prob. 90PCh. 20 - Prob. 91PCh. 20 - Prob. 92PCh. 20 - Prob. 89PCh. 20 - Prob. 93PCh. 20 - Prob. 94PCh. 20 - Prob. 95PCh. 20 - Prob. 96PCh. 20 - Prob. 97PCh. 20 - Prob. 98PCh. 20 - Prob. 99PCh. 20 - Prob. 100P
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