24 Hour Clock

We normally use 12-hour clock system. The hour hand of the clock goes round the dial twice a day (24 hours). Some departments like railways, Airlines, etc use 24-hour clock system because they do not use a.m. and p.m. times.


In a 24-hour clock system, we express time in four digits. The first two digits represent hours and the last two digits represent the minutes.

On the dial there are two concentric circles. The inner circle has 1 to 12 numbers while the outer circle has 13 to 24 numbers.

24 Hour Clock

In a 24-hour clock system, we start counting the time from midnight. Let us understand 24-hour system by considering some examples.  

(i) 12 midnight is denoted by 24 00 hours or 00 00 hour.

(ii) 12 noon is denoted by 12 00 hours.

(iii) 6 in the morning is denoted by 06 00 hours.

(iv) 10:25 in the evening is denoted by 22 25 hours. 
(10:25 + 12:00)

(v) 7:15 in the evening is denoted by 19 15 hours. 
(7:15 + 12:00)

From the above examples, we can conclude that between 12 midnight and 12 noon the 24-hour clock time is same.

For example, 10 40 hours = 10:40 a.m., 08 20 hours = 8:20 a.m., 11 30 hours = 11:30 a.m.

But between 12 noon and 12 midnight to convert the 24-hour clock time into 12-hour clock time, we subtract 12 from the 24-hour time.

For example, 19:30 hours = 19:30 – 12:00 = 7:30 p.m.

Similarly, to convert the 12-hour clock time into 24-hour clock time between 12 noon and 12 midnight, we add 12.

For example, 11:30 p.m. = 11:30 + 12:00 = 23:30 hours.


Therefore, the time which is shown by the inner circle is the time before noon and that shown by the outer circle is the time after noon.


These are some more examples:

After midnight          00:10 a.m. is shown as 00:10

                              02:45 a.m. is shown as 02:45

                              10:48 a.m. is shown as 10:48

                              02:45 p.m. is shown as 14:45

                              10:48 p.m. is shown as 22:48


               Clock                General Time                  24 hour clock

General Time

00:00 midnight

(Just after midnight) 

or, 

12:00 midnight



06:00 a.m.(6 hours zero minutes in the morning)






12:00 noon 

00:00

(Just after midnight) or,

24:00 hours





06:00







12:00

Time after noon


06:10 p.m. 







08:30 p.m.






10:45 p.m.



18:10







20:30






22:45


We know how to use a.m. and p.m. to represent the time of the day in 12-hour clock. We know that a.m. is used to express time between 12 o’clock mid night to 12 o’clock noon and p.m. is used to express time between 12 o’clock noon to 12 o’clock midnight.

In 24-hour clock time, we express time in four digits. The first two digits from left represt hours and the last two digits represent the minutes.

So, to express time for a.m., we just write the time without separating hours and minutes.

For example 7:45 am is written as 0745 hours.

To express time for p.m. we add 12 to the hours and then write hours and minutes without separating them. For example 6:30 p.m. is written as (6 + 12), 1830 hours.


Questions and Answers on 24 Hour Clock:

I. Convert the time given in a.m. and p.m. form into the 24-hour form. One is shown as an example.

(i) 1 : 24 p.m.

1 : 24 p.m. = 1 : 24 + 12 : 00

                    = 13 : 24

1 : 24 p.m. = 1324 hours


(ii) 7 : 16 a.m.

(iii) 4 : 55 a.m.

(iv) 6 : 54 p.m.

(v) 9 : 33 p.m.

(vi) 11 : 42 p.m.


Answers:

I. (ii) 0716 hours

(iii) 0455 hours

(iv) 1854 hours

(v) 2133 hours

(vi) 2342 hours



II. Convert the time given in 24- hour form into a.m./p.m. form. One is shown as an example.

(i) 1341 hours

1341 = 1341 – 1200

          = 1 : 41 p.m.

1341 = 1 : 41 p.m.

(ii) 2325 hours

(iii) 1750 hours

(iv) 0853 hours

(v) 0432 hours

(vi) 1539 hours


Answers:

II. (ii) 11 : 25 p.m.

(iii) 05 : 50 p.m.

(iv) 08 : 53 a.m.

(v) 04 : 32 a.m.

(vi) 03 : 39 p.m.


III. Write the correct 24-hour clock time with each analog clock.

24 Hour Clock Worksheet

Answers:

III. (i) 1535 hours

(ii) 0505 hours

(iii) 2015 hours

(iv) 0400 hours

(v) 0150 hours

(vi) 2020 hours

(vii) 2230 hours

(viii) 1955 hours

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