2)Battery-powered electricity is very expensive compared with that available fro

Question

2)Battery-powered electricity is very expensive compared with that available from a wall receptacle.

a)Estimate the cost per kWh of an alkaline D-cell (cost $1.70). This battery can provide a continuous current of 27 mA for 850 h at 1.5 V .

b)Estimate the cost per kWh of an alkaline AA-cell (cost $1.25). This battery can provide a continuous current of 27 mA for 120 h at 1.5 V . c)Compare to normal 120-V ac house current at $0.10/kWh (answer in a ratio)

3)A neuron is stimulated with an electric pulse. The action potential is detected at a point 3.60 cm down the axon 0.0053 s later. When the action potential is detected 7.10 cm from the point of stimulation, the time required is 0.0061 s . What is the speed of the electric pulse along the axon?

Explanation / Answer

Solution:

a) Current = I = 27 mA = 0.027 A

Voltage = 1.5 V

Power = VI = 1.5 x 0.027 = 0.0405 Watts = 0.0405 x 10^-3 kW

Energy = power x time = (0.0405 x 10^-3 )(850) = 0.0344 kw-h

cost per kW h = 1.70 /0.0344 = $49.4 /kwh

b) Cost per kW-h = total cost / power x time = (1.25) / (120*0.027x10^-3) = $257.2/kwh

c) the same 27mA current and V = 120 V will give

energy = V I t /1000 kwh =

0.027 * 120* 120 *10^-3 kWh energy = 0.3888 kwh

cost = 0.1 / 0.3888 = $0.257 /kWh

Ratio = 257.2 / 0.257

3) Speed = (d2-d1) / (t2-t1) = ( 7.10 - 3.60) / ( 0.0061 - 0.0053) = 4375 cm/s

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