- #1
Masafi
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Hi, I need help with the last part. I have put each part with the answers.
For b) ii) I want to know where does V=1.6 V come from?
(a) A 2200 µF capacitor is charged to a potential difference of 12 V and then discharged through an electric motor. The motor lifts a 50 g mass through a height of 24 cm.
(i) Show that the energy stored in the capacitor is approximately 0.16
E = ½ CV^2 = 0.5 × 2200 × 10(–6) F × (12 V)^2
E = 0.158 J
(ii) What is the efficiency of the electric motor in this situation?
E = mgh = 0.12 J
Efficiency = 0.12 ÷ 0.16 J = 0.75
(b) The capacitor is charged to 12 V again and then discharged through a 16 resistor.
(i) Show that the time constant for this discharge is approximately 35 ms.
t = RC = 35.2 s
---- I need help with ----
(ii) Sketch a graph of current against time for this discharge on the grid below. You should indicate the current at t = 0 and t = 35 ms.
Curve starting on I axis but not reaching t axis
I = 1.6 V / 16Ohms = 100 mA shown on axis
Curve passing through about 37 mA at t = 35 ms
For b) ii) I want to know where does V=1.6 V come from?
(a) A 2200 µF capacitor is charged to a potential difference of 12 V and then discharged through an electric motor. The motor lifts a 50 g mass through a height of 24 cm.
(i) Show that the energy stored in the capacitor is approximately 0.16
E = ½ CV^2 = 0.5 × 2200 × 10(–6) F × (12 V)^2
E = 0.158 J
(ii) What is the efficiency of the electric motor in this situation?
E = mgh = 0.12 J
Efficiency = 0.12 ÷ 0.16 J = 0.75
(b) The capacitor is charged to 12 V again and then discharged through a 16 resistor.
(i) Show that the time constant for this discharge is approximately 35 ms.
t = RC = 35.2 s
---- I need help with ----
(ii) Sketch a graph of current against time for this discharge on the grid below. You should indicate the current at t = 0 and t = 35 ms.
Curve starting on I axis but not reaching t axis
I = 1.6 V / 16Ohms = 100 mA shown on axis
Curve passing through about 37 mA at t = 35 ms