JAMB and WAEC Physics questions: Simple a.c. circuits

17 questions with answers and explanations. Tap an option to check yourself.

1. Question 1· Simple a.c. circuits· WAEC

   The reactance of a capacitor decreases when the frequency of the supply

   • Astays the same
   • Bdecreases
   • Cincreases
   • Dbecomes zero

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   Explanation and discussion

2. Question 2· Simple a.c. circuits· WAEC

   Find the reactance of a 0.7 H inductor on a 50 Hz supply. [π = 22/7]

   • A110 Ω
   • B220 Ω
   • C35 Ω
   • D440 Ω

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   Explanation and discussion

3. Question 3· Simple a.c. circuits· WAEC

   The frequency of the public electricity supply in Nigeria is

   • A50 Hz
   • B60 Hz
   • C100 Hz
   • D240 Hz

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   Explanation and discussion

4. Question 4· Simple a.c. circuits· JAMB

   In a purely capacitive a.c. circuit, the current

   • Ais zero
   • Blags behind the voltage by 90°
   • Cis in phase with the voltage
   • Dleads the voltage by 90°

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   Explanation and discussion

5. Question 5· Simple a.c. circuits· JAMB

   The reactance of a capacitor in an a.c. circuit

   • Adoes not depend on frequency
   • Bincreases as the frequency increases
   • Cdecreases as the frequency increases
   • Dis always zero

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   Explanation and discussion

6. Question 6· Simple a.c. circuits· WAEC

   An alternating current has a peak value of 10√2 A. Its r.m.s. value is

   • A10 A
   • B20 A
   • C14.1 A
   • D5 A

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7. Question 7· Simple a.c. circuits· JAMB

   An inductor in an a.c. circuit

   • Aopposes changes in the current through it
   • Bstores charge on plates
   • Cconverts a.c. to d.c.
   • Dhas no effect

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8. Question 8· Simple a.c. circuits· JAMB

   Find the peak voltage of a 230 V r.m.s. supply.

   • A230 V
   • B163 V
   • C325 V
   • D460 V

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   Explanation and discussion

9. Question 9· Simple a.c. circuits· WAEC

   The peak value of an alternating current is 10√2 A. Find its r.m.s. value.

   • A14.1 A
   • B20 A
   • C10 A
   • D5 A

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   Explanation and discussion

10. Question 10· Simple a.c. circuits· WAEC

    The unit of inductive reactance is the

    • Aohm
    • Bhenry
    • Cfarad
    • Dhertz

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11. Question 11· Simple a.c. circuits· JAMB

    The reactance of an inductor in an a.c. circuit increases when the frequency

    • Adecreases
    • Bincreases
    • Cis kept constant
    • Dfalls to zero

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    Explanation and discussion

12. Question 12· Simple a.c. circuits· JAMB

    The r.m.s. value of the mains supply is 240 V. Find its peak value.

    • A480 V
    • Babout 170 V
    • C240 V
    • Dabout 339 V

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    Explanation and discussion

13. Question 13· Simple a.c. circuits· JAMB

    An alternating voltage has a peak value of 10√2 V. Find its r.m.s. value.

    • A5 V
    • B20 V
    • C14.1 V
    • D10 V

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    Explanation and discussion

14. Question 14· Simple a.c. circuits· WAEC

    In a purely resistive a.c. circuit, the current and voltage are

    • A180° out of phase
    • B90° out of phase
    • Cin phase
    • Dalways zero

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    Explanation and discussion

15. Question 15· Simple a.c. circuits· WAEC

    In a purely inductive a.c. circuit, the current

    • Ais always zero
    • Bleads the voltage by 90°
    • Cis in phase with the voltage
    • Dlags the voltage by 90°

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    Explanation and discussion

16. Question 16· Simple a.c. circuits· WAEC

    The r.m.s. value of an a.c. voltage with peak 340 V is about

    • A240 V
    • B340 V
    • C480 V
    • D170 V

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    Explanation and discussion

17. Question 17· Simple a.c. circuits· JAMB

    The frequency of the mains a.c. supply in Nigeria is

    • A100 Hz
    • B60 Hz
    • C220 Hz
    • D50 Hz

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    Explanation and discussion