Using the formula mA x seconds = mAs, add the missing information. Make sure you convert milliseconds to seconds where required! 300 mA at 20 millisecs mAs 100 mA at 2/5 sec = mAs 400 mA at 0.15 sec= mAs mA at 30 millisecs = 60 mAs mA at 1/40 sec = 5 mAs mA at 0.25 sec = 10 mAs 500 mA at sec = 25 mAs 100 mA at sec = 10 mAs 200 mA at sec = 75 mAs
The Correct Answer and Explanation is:
Here are the correct answers to complete the table:
| 300 mA at 20 millisecs | = 6 mAs |
| 100 mA at 2/5 sec | = 40 mAs |
| 400 mA at 0.15 sec | = 60 mAs |
| 2000 mA at 30 millisecs | = 60 mAs |
| 200 mA at 1/40 sec | = 5 mAs |
| 40 mA at 0.25 sec | = 10 mAs |
| 500 mA at 0.05 sec | = 25 mAs |
| 100 mA at 0.1 sec | = 10 mAs |
| 200 mA at 0.375 sec | = 75 mAs |
Explanation
The calculations are based on the fundamental formula for radiographic exposure: milliamperes (mA) × exposure time (seconds) = milliampere-seconds (mAs). This formula allows us to find any one of the three values if the other two are known. A critical step for some of these problems is converting milliseconds to seconds, which is done by dividing the number of milliseconds by 1000.
Calculating mAs (Rows 1-3):
- Row 1: First, convert 20 milliseconds to seconds: 20 ÷ 1000 = 0.02 seconds. Then, multiply by the mA: 300 mA × 0.02 s = 6 mAs.
- Row 2: Convert the fraction 2/5 to a decimal: 2 ÷ 5 = 0.4 seconds. Then, calculate the mAs: 100 mA × 0.4 s = 40 mAs.
- Row 3: The time is already in seconds. Simply multiply the values: 400 mA × 0.15 s = 60 mAs.
Calculating mA (Rows 4-6):
To find the missing mA value, we rearrange the formula to: mA = mAs ÷ seconds.
- Row 4: Convert 30 milliseconds to seconds: 30 ÷ 1000 = 0.03 seconds. Then, divide the mAs by the time: 60 mAs ÷ 0.03 s = 2000 mA.
- Row 5: Convert the fraction 1/40 to a decimal: 1 ÷ 40 = 0.025 seconds. Then, solve for mA: 5 mAs ÷ 0.025 s = 200 mA.
- Row 6: The time is in seconds. Divide the mAs by the time: 10 mAs ÷ 0.25 s = 40 mA.
Calculating Seconds (Rows 7-9):
To find the missing time in seconds, we again rearrange the formula to: seconds = mAs ÷ mA.
- Row 7: Divide the mAs by the mA: 25 mAs ÷ 500 mA = 0.05 seconds.
- Row 8: Divide the mAs by the mA: 10 mAs ÷ 100 mA = 0.1 seconds.
- Row 9: Divide the mAs by the mA: 75 mAs ÷ 200 mA = 0.375 seconds.
