A 9 volt battery powers a portable radio. The radio draws a current of 150 milli

Question

A 9 volt battery powers a portable radio. The radio draws a current of 150 milliamperes. What is its resistance The resistance of a flashlight bulb is 11.5 ohms when it is lighted. How much current must a 6 volt lantern cell provide it for proper operation To operate properly, a voltmeter must be placed (choose one) across the element to be measured between the element to be measured and the rest of the circuit on top of the element to be measured To operate properly, an ammeter must be placed (choose one) across the element to be measured between the element to be measured and the rest of the circuit on top of element to be measured The resistance of a light bulb filament increases when it heats up. How do you expect the resistance values at currents of 0.5 A and 1.0 A to compare

Explanation / Answer

Part 1

We use ohm's law

V = I R      R= V /I        

R = 9 / 150 10-3

R = 60 W

Part 2

The same expression is used

V = I R         I= V / R

I= 6 / 11.5

I = 0.5217 A   = 521.7 mA

Part 3

A voltmeter operation requires to connect in parallel with the element to be measured, therefore the answer must be "c"

Part 4

Resistance increases with temperature according to the expression of resistivity

R= Ro ( 1 + alfa (T-To))           1

Where   alfa is the coefficient of linear expansion, that of the order of 10-6 ° C - 1)

The expression of power in an element

P = V I                2

V= I R        P= I2 R

Substituting equation 2

P1= 0.52 R1 = 0.25 R1

P2 = 12 R2 = 1 R2

Where we see that the power dissipated in the resistance rises a de facto from 4 to duplicate the current, therefore the effect joule, heat, on the wire must also upload this factor by which one would expect an increase of the temperature of this order and therefore equal increase in resistance

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