How to use Electricity Formulas?

Electricity formulas

Given on the exam…• V=RI• P=VI• E=P∆t

V = Potential differenceR = ResistanceI = IntensityE = Energy∆t = Time

5 Steps to formula success

1. What are we looking for?2. Choose formula (What else are we given?)3. Rewrite appropriate formula4. Do we need other formulas?5. Replace the variables and solve

Example 1

1. What are we looking for?- Potential difference (V)

Example 1

2. Choose the formula(what are we given?)

• V=RI• P=VI• E=P∆t

R

I

Example 1

3. Rewrite the appropriate formula?

V= RI

Example 1

4. Do we need another formula?

Not in this case

Example 1

5. Replace values and solveV = R IV = 25 Ω * 10 AV = 250 V

Example 2

1. What are we looking for?- Time (∆t)

Example 2

2. Choose the formula(what are we given?)

• V=RI• P=VI• E=P∆t

P E

Example 2

3. Rewrite the appropriate formula?

E= P∆t ∆t = E/P

Example 2

4. Do we need another formula?

Not in this case

Example 2

5. Replace values and solve∆t = E/P∆t = 30 000 J / 2000 W∆t = 15 sec

Example 3

1. What are we looking for?- Energy (E)

Example 3

2. Choose the formula(what are we given?)

• V=RI• P=VI• E=P∆t

VI t

Example 3

3. Rewrite the appropriate formula?

E= P∆t

Example 3

4. Do we need another formula?Yes, To only use E=Pt I am missing P

I can find it using P=VI

Example 3

5. Replace values and solveE = P∆tE = P (30 *60 seconds)

P = VIP = 220 V * 50 AP = 11 000 W

E = 11 000 W *1800 secondsE = 19 800 000 J (or 5,5 kwH if you use hours instead of seconds

Thank you

• So remember…– Find what we are looking for– Choose your formula or formulas based on the

information given to you– Rewrite the formula– Verify if other formulas are needed– Replace the values and solve

GOOD LUCK !!!!