The frequency of an alternating current is 50 Hz. In how much time does it reverse its direction?

CONCEPT:

• Alternating current: The electric current whose direction changes periodically is called electric current.

• Frequency (ν): The number of waves that pass a given point per second is called frequency.
  • The unit of frequency is vibration per second or Hertz.

• Time period (T): The time taken to complete one full oscillation or cycle by the Wave is called time period.

  • The SI unit of the time period is second (s).

The relationship between time period and frequency is given as:

Time period (T) = 1/ν 

EXPLANATION:

Given that:

Frequency (ν) = 50 Hz

Time period (T) = 1/ν = 1/50 sec

So the time taken to complete one oscillation = 1/50 sec

Since this time is the time for one complete oscillation, but the current changes its direction at midpoints (half-wave) itself. 

So time for reverse the direction = T/2 = 1/100 sec

Hence option 2 is correct.

Mistake PointsThe important point to note here is that 1/50 is the time for one complete oscillation. But we are asked to find the time at which the current changes its direction (from positive to negative. And this happens at midpoints (half-wave) itself. 

So time for reverse the direction = T/2 = 1/100 sec