Electrical Power - Equation Questions:

In summary, a 1.5V rechargeable cell labelled 2300 mA h can supply 2300 mA for one hour. When calculating its energy storage in mWh and J, it is equivalent to 3450 mWh and 12.42 kJ respectively. When connected in series, four of these cells can light a bulb labelled 6.0V and 120 mA for 19.2 hours.
  • #1
I-need-help
15
0
A 1.5V rechargeable cell is labelled 2300 mA h. This means that it can supply the equivalent of 2300 mA for one hour.

b) How much energy does the cell store in:
i- mWh?
ii- J?

and c) How long can four cells, connected in series, light the bulb?

for b) i- I got: W = V x Q, so W = V x I x t

W = 1.5V x 2.3A x 1second
= 3.45W = 3450mWh​

b) ii-
W = Js-1
J = W x t
J = 3.45 x 60 x 60
J = 12420 = 12.42kJ​


I know that I got b (i) and (ii) correct, expect I'm stuck on c). The previous sub-questions are just supplied to give more information :) Thanks
 
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  • #2
What are the characteristics of the bulb (its wattage or current requirement)?
 
  • #3
gneill said:
What are the characteristics of the bulb (its wattage or current requirement)?

Ah yeah, missed out some info. The bulb is labelled 6.0 V and 120mA... no wattage, but you could work that out, so P = 6V x 0.12W = 0.72W
 
  • #4
You know that each cell will be depleted after one hour supplying 2300 mA. The bulb requires 120 mA. How long will they last at that rate?
 
  • #5
Each cell will last... 2300mA shared by 120 mA ... so, 19.2 hours. And that's the right answer in the back of the book... wow. Hmm. Thanks! That is right isn't it? The textbook isn't always necessarily correct.
 
  • #6
Yup. That's right.
 
  • #7
Ah thanks again gneill!
 

1. What is the equation for electrical power?

The equation for electrical power is P = VI, where P represents power in watts, V represents voltage in volts, and I represents current in amperes.

2. How is electrical power measured?

Electrical power is measured in watts (W), which is the product of voltage (V) and current (I).

3. Can the electrical power equation be applied to both AC and DC circuits?

Yes, the electrical power equation can be applied to both AC (alternating current) and DC (direct current) circuits, as long as the values for voltage and current are consistent with the type of circuit being analyzed.

4. What is the relationship between electrical power and energy?

Electrical power is the rate at which energy is transferred or used, and is measured in watts. Energy, on the other hand, is the amount of work that can be done by that power over a period of time, and is measured in joules (J). The relationship between power and energy is given by the equation E = Pt, where E represents energy, P represents power, and t represents time.

5. How does resistance affect electrical power?

According to Ohm's Law, the relationship between voltage (V), current (I), and resistance (R) is given by the equation V = IR. This shows that as resistance increases, the voltage and current decrease, and therefore the electrical power decreases as well. This is because resistance acts as an obstacle to the flow of electrical current, causing a decrease in the amount of power that can be delivered to a circuit.

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