In a cyclotron, charged particles, or ions, are accelerated inside an

Question

In a cyclotron, charged particles, or ions, are accelerated inside an evacuated tank, to prevent them from colliding with air molecules and being scattered. The vacuum tank is placed between the poles of an electromagnet, which creates a field that bends the ion beam into a circular orbit between two accelerating electrodes, or “dees.” Because the ions carry a positive electric charge, they are attracted toward the dee, which is electrically negative at the moment. Were it not for the magnetic field, the ions would be accelerated in a straight line; instead, they are deflected into a circular path back toward the dee gap. By the time the ions again reach the dee gap, the sign of the electric potential on the dees is reversed, so that now the ions are attracted toward the opposite dee. As this process of alternating the electric potential is repeated, the ions gain speed and energy with each revolution. This causes them to spiral outward in a  regular  manner. Finally, they strike a target inserted into their path or are extracted from the cyclotron for use as an external beam.    1 
 1. Based on the information presented in the passage, which of the following most closely represents the sequence of events describing the path of an ion in a cyclotron?

A. A positively charged ion is repelled from a negative dee, then attracted to a positive dee.
B. A negatively charged ion is attracted to a positive dee, then repelled by a negative dee.
C. A positively charged ion is attracted to a negative dee, then attracted by a magnetic field.
D. A positively charged ion is attracted to a negative dee, then attracted to a negative dee.
E. A positively charged ion is attracted to a negative dee, which reverses the ion’s electric potential.

2 
 2. In the context in which it appears, “regular” most nearly means

A. normal
B. agreeable
C. average
D. predictable
E. useful

3 
 3. The author of the passage mentions the magnetic field primarily in order to

A. argue that the magnetic field is less important than the dee gap in cycling the ions
B. suggest that ions would accelerate to dangerous speeds without a magnetic field
C. provide support for the notion that, in nature, ions tend to travel in straight lines
D. cast doubt on the hypothesis that ions tend to travel elliptically once deflected
E. indicate the necessity of deflecting the ions back toward the dee gap

Sajjad1994 · Answer

Official Explanation

1. Based on the information presented in the passage, which of the following most closely represents the sequence of events describing the path of an ion in a cyclotron?

The passage explains that the ions, which are positive, are attracted to the negative dee, then again attracted to a negative dee after the dee’s electric potential has been reversed. 
  
  Answer: D

Sajjad1994 · Answer

Official Explanation

2. In the context in which it appears, “regular” most nearly means

Explanation

It can be inferred from the context that the author believes that the ions in the cyclotron act in a predictable way because their behavior is described chronologically and authoritatively; the author therefore uses  “regular”  to mean  “predictable.”  
 
  Answer: D

Sajjad1994 · Answer

Official Explanation

3. The author of the passage mentions the magnetic field primarily in order to

The author explains the magnetic field as a tool with which to direct the ions back toward the dee gap; he is therefore indicating the necessity of that direction for the operation of the cyclotron 
 
  Answer: E

mkeshri185 · Answer

I didn't get why D is the answer...

By the time the ions again reach the dee gap, the sign of the electric potential on the dees is reversed, so that now the ions are attracted toward the opposite dee
 It is given in the passage.

It says ion was +ve and it get attracted towards -ve dee . So first part is fine

Now passage says Electric potential on Dees is reversed. Which means now they are +ve dees. How can ions get attracted to -ve dee again?

Sajjad1994 · Answer

Start:

Dee A = negative, Dee B = positive. 
 Positive ion ----> attracted to Dee A (negative).

Ion moves inside Dee A (magnetic field bends it in semicircle), emerges at gap.

Electric potential reverses:

Now Dee A = positive, Dee B = negative.  
 
 Ion -----> attracted to Dee B (which is now negative).   
 
So in one full cycle (gap ---> Dee A ---> gap ---> Dee B):

First half:  attracted to negative Dee A. 
  Second half:  attracted to negative Dee B.  
 
What  (D)  says

(D) A positively charged ion is attracted to a negative dee, then attracted to a negative dee.

“Then”  here means after one half-turn, the second attraction is to the other dee, which is negative after reversal. So yes, both times it’s attracted to a negative dee, just a different dee each half-revolution.

The passage says after reversal  “ions are attracted toward the opposite dee”  that opposite dee is now negative (because potentials swapped).

So  (D)  is consistent, while others are factually wrong.

In a cyclotron, charged particles, or ions, are accelerated inside an

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