- A cloud is at a potential of 2 x 104 V relative
to the ground. When lightning strikes the
ground, a charge of 86 C is transferred to the
ground. Calculate the work done.
Answers
Explanation:
An electric field stronger than 3.0 x 106 V/m will cause sparks to occur in air. What is the maximum potential difference that can be applied across two metal plates 1.0 mm apart before sparking begins ?
V = Eh = 3.0 x 106 x 1.0 x 10-3 = 3000 Volts
A cloud is at a potential of 8.0 x 106 V relative to the ground. A charge of 40 C is transferred in a lightning stroke between the cloud and the ground. Find the energy dissipated.
Energy dissipated = QV = 40 x 8.0 x 106 = 3.2 x 108 J
In charging a 20 kg storage battery, a total of 2.0 x 105 C is transferred from one set of electrodes to another. The potential difference between the electrodes is 14 V.
(a) How much energy is stored in the battery ?
Electrical PE = QV = 2.0 x 105 x 14 = 2.8 x 106 J
(b) If this energy were used to raise the battery above the ground, how high would it go ?
mgh = PE electrical
h = PE/mg
h = 2.8 x 106/ (20 x 9.8) = 1.43 x 104 m = 14.3 km
(c) If this energy were used to provide the battery with kinetic energy, what would its speed be ?
KE = PE electrical
½mv2 = 2.8 x 106
v2 = (2.8 x 106 x 2)/m = (2.8 x 106 x 2)/20
v = 530 m/s
A potential difference of 20 kV is used to accelerate electrons in a television picture tube.
(a) How much kinetic energy do the electrons acquire ?
Electrical PE lost = KE gained
QV = KE = ½mv2
KE = 1.6 x 10-19 x 20000
KE = 3.2 x 10-15 J
(b) What is their speed ?
KE = ½mv2
v2 = 2(KE)/m = (2 x 3.2 x 10-15 )/9.1 x 10-31
v = 0.84 x 108 m/s
Answer:
1.72 × 10⁶ J
Explanation:
work done = potential difference × charge moved
= 2 × 10⁴ V × 86 C
= 172 × 10⁴ J
= 1.72 × 10⁶ J