A cylindrical tungsten filament 15.0 cm long with a diameter of 1.20 mm is to be

Question

A cylindrical tungsten filament 15.0 cm long with a diameter of 1.20 mm is to be used in a machine for which the temperature will range from room temperature (20 C) up to 120 C. It will carry a current of 12.0 A at all temperatures ( Resistivity of tungsten at 20 C is 5.25×108m , the temperature coefficient of resistivity at 20 C is 0.0045 C1 )

Part A

What will be the maximum electric field in this filament?

Express your answer using two significant figures.

Part B

What will be its resistance with that field?

Express your answer using two significant figures.

Part C

What will be the maximum potential drop over the full length of the filament?

Express your answer using two significant figures.

Explanation / Answer

the maximum electric field in this filament is

rho = E/J

E = rho J= r_0 ( 1+ alpha ( T-Ti) ( I/A)

=5.25×108m (1+ 0.0045 C1 ( 120-20) (12/ PI( 0.0006)^2

=0.81 V/m

(C)

V_max = Ed = 0.81 V/m ( 0.15) = 0.12 V

(b)

R = V/I = 0.1212/12 A = 0.010 A

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.