alternating-currents Question 5
Question: Q. 2. State which of the two a capacitor or an inductor, tends to become SHORT when the frequency of the applied alternating voltage has a high value.
U] [CBSE SQP 2014]
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Solution:
Ans. The capacitor. [CBSE Marking Scheme 2014]
Detailed Answer :
Between inductor and capacitor, the capagitor will act short at high frequencies while will act open at low frequencies. So at high frequencies, capacitor has time to get a very less amount of charge while at low frequencies, there is tot of time for capacitor to collect considerable amount of charge which shows presence of large feyerse voltage. Hence the sum of the voltages of dapacitor and $a c$ source will be nearly zero which shows current also to be nearly zero.
[AI Q. 3. Why is the use of $a c$ voltage preferred over $d c$ voltage ? Give two reasons. $R$ [OD. I, II, III 2014]
Ans. Any two of the following (or any other correct) reasons :
(i) ac can be transmitted with much lower energy losses as compared to $d c$.
(ii) ac voltage can be adjusted (stepped-up or stepped down) as per requirement.
(iii) ac current in a circuit can be controlled using (almost) wattless devices like choke coil.
(iv) $a c$ is easier to generate.
[CBSE Marking Scheme 2014] 1/1/2 +1/2
[AI Q. 4. Plot a graph showing variation of capacitive reactance with the change in the frequency of the ac source.
