To reverse the output polarity of a DC generator you reverse the
[ Select ]
field leads
current
voltage
direction of rotation
or
[ Select ]
Armature leads
rotation
magnets
current
but not both.

Question

To reverse the output polarity of a DC generator you reverse the 
[ Select ]
field leads
current
voltage
direction of rotation
 or 
[ Select ]
Armature leads
rotation
magnets
current
   but not both.

BlackTom AI · Accepted Answer

Fleming’s Right‑Hand Rule for generators: the induced EMF (and thus output polarity at the generator terminals) depends on the direction of the magnetic field and the direction of conductor motion. Changing either the magnetic field polarity or the way the armature is connected to the external terminals will reverse the measured output polarity; changing both at once cancels the effect.

1) Relevant concepts
- Induced EMF direction is determined by the cross‑product of conductor velocity and magnetic field (Fleming’s Right‑Hand Rule).  
- “Field leads” refers to the connections that set the magnetic field polarity. Reversing them flips the field direction inside the machine, which reverses induced EMF sign.  
- “Armature leads” refers to the external connections (or brush/terminal wiring) from the armature. Swapping those leads reverses which terminal is positive/negative without changing the internal generation sign.

2) Step‑by‑step reasoning
- Start with a reference: terminal A is + with respect to B because of field direction and armature wiring.  
- Case 1: Reverse the field leads (flip the magnetic field). The induced EMF in the armature reverses sign, so terminal A becomes negative relative to B. Polarity is reversed.  
- Case 2: Leave field as original but reverse the armature leads (swap the output wires or brushes). The internal EMF is unchanged but the terminal labels are swapped, so the terminal that was + is now connected as – relative to the other terminal — measured polarity reverses.  
- If you reverse both field leads and armature leads: reversing the field changes EMF sign, and reversing the armature leads swaps terminals; these two reversals multiply to restore the original terminal polarity (double reversal cancels).

3) Intermediate/equation style illustration
- Let internal EMF = +E (A positive relative to B).  
- Field reversed → internal EMF = −E. Terminal mapping unchanged → observed = −E.  
- Armature leads reversed → mapping swapped → observed = −E.  
- Both reversed → internal EMF = −E and mapping swapped → observed = +(E) (original).

4) Why the correct answer is correct
Reversing the field leads directly flips the generated EMF sign; reversing the armature leads swaps the terminal outputs. Each action alone reverses the measured polarity. Doing both reversals cancels the effect, so the instruction “but not both” is satisfied by the pair field leads and Armature leads.

5) Why other options are incorrect
- Current/voltage: these are results of the generator action; you don’t “reverse” source current or voltage leads in the same conceptual way asked here.  
- Direction of rotation/rotation: changing rotation direction would also reverse EMF, but the question’s standard pairing refers to wiring/lead reversals (field or armature), not mechanical reversal.  
- Magnets: physically reversing magnets is equivalent to reversing the field but the conventional phrase in this context is “field leads,” and the question expects electrical lead reversal options.

Conclusion: Reversing either the field leads or the armature leads (but not both) will reverse the output polarity. This matches the provided answer: field leads and Armature leads.

To reverse the output polarity of a DC generator you reverse the [ Select ] field leads current voltage direction of rotation or [ Select ] Armature leads rotation magnets current but not both.多重下拉选择题

类似问题

A use for a separate excited DC generator would be in a moving coil meter.

A separately excited DC generator would be a:

Which of the below is NOT a type of DC generator?

The image below is of a :

A commutator is to ensure the [ Select ] input stator output field winding from the generator is [ Select ] AC backwards rectified DC and not [ Select ] AC low high Reversed .

“Involves changing an operational system to make it more efficient, reliable, and maintainable”. Which of the following are the internal factors that cause system request? i. User request ii. Customer iii. Existing system iv. Technology

Which of the following practices is NOT recommended when naming variables?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单