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Flashcards in electricity calculations Deck (6)
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energy transfered

and power formulae

energy transfered = power x time kWh   E = P  x T

 E = P × t when: E is the energy transferred in joules, J P is the power in watts, W T is the time in seconds, s. MAY HAVE TO CONVERT MINUTES BY X 60



I      V

P = power in Watts

I =Amps

V = Voltage


calculating power


W = V X Amps

Power is measured in watts, W Voltage (potential difference) is measured in volts, V Current is measured in amperes (amps), A For example, what is the power of a 5 A 1.5 V lamp? Power = 5 × 1.5 = 7.5 W


We've seen the formula for determining the power in an electric circuit: by multiplying the voltage in "volts" by the current in "amps" we arrive at an answer in "watts." Let's apply this to a circuit example:

In the above circuit, we know we have a battery voltage of 18 volts and a lamp resistance of 3 Ω. Using Ohm's Law to determine current, we get:

I = E/R   18V/3 R  =6A


Now that we know the current, we can take that value and multiply it by the voltage to determine power:


Answer: the lamp is dissipating (releasing) 108 watts of power, most likely in the form of both light and heat.


formula for resistivity

R = ρl/A


R = resistance (Ω)

ρ = resitivity of the material (Ω m)

I = length of wire (m)

A = cross-sectional area of the wire (m2)


for calculations current is measured in.....

AMPS !!!!


resistivity with temperature

Rt  =  Ro (1 =at )

Rt= final resistance of coil when heated to t degrees C in Ohms

Ro= Resistamce of coil at 0 gegrees C in Ohms

a ( should be alpha sign ) temp coefficient of resistance of a material in Ohms per degree c

t = final temp in degress centigrade