SME
Circuit Analysis I · Problem type
Power absorbed or delivered
Use this for “An element has 5 V across it and −2 A into its + terminal. Does it absorb or deliver power?”
Diagram
P = VI = +5 V × (−2 A) = −10 W
Negative: the element delivers power (a source).
This is an example. Type your own values to start a new problem.
P (W)
=
V (V)
×
(
I (A)
)
Formulas
P
=
V
×
I
−10 = 5 × (−2)
Assumptions
•
Passive sign convention: the current I is the current entering the element’s + terminal.
•
P > 0 means the element absorbs power; P < 0 means it delivers power to the circuit.
•
The powers absorbed by all the elements of a circuit add to 0.
Step-by-step
WE KNOW
V = +5 V, I = −2 A
FIND
power absorbed (P)
Step 1 · Find power absorbed (P)
Use P = V × I
Voltage
times
the
current
into
+;
P
<
0,
so
the
element
delivers
power.
P
=
5
×
(−2)
P
=
−10
W
Check
Put the numbers back in. Both sides should match.
−10 = 5 × (−2) ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.