الفيزياء العامة الجزء الثاني#موقع الفيزياء.كوم

Current & Resistance
7.6 Electrical Energy and Power
The current can flow in circuit when a
battery is connected to an electrical device
through conducting wire as shown in
figure 7.3. If the positive terminal of the
battery is connected to a and the negative
terminal of the battery is connected to b of
the device. A charge dq moves through
the device from a to b. The battery
perform a work dW = dq V ab . This work
is by the battery is energy dU transferred
to the device in time dt therefore,
I
Battery
I
I
I
Figure 7.3
Aa
Ab
I
I
dU=dW= dq V ab =I dt V ab (7.13)
The rate of electric energy (dU/dt) is an electric power (P).
dU
P = = IV ab
(7.14)
dt
Suppose a resistor replaces the electric device, the electric power is
P = I 2 R (7.15)
2
V
P = (7.16)
R
The unit of power is (Joule/sec) which is known as watt (W).
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