# 25 - CURRENT RESISTANCE AND ELECTROMOTIVE FORCE 25 25.4(a...

This preview shows pages 1–2. Sign up to view the full content.

C URRENT , R ESISTANCE , AND E LECTROMOTIVE F ORCE 25.4. (a) IDENTIFY: By definition, J = I/A and radius is one-half the diameter. SET UP: Solve for the current: I = JA = J π( D /2) 2 EXECUTE: I = (1.50 10 6 A/m 2 )( π )[(0.00102 m)/2] 2 = 1.23 A EVALUATE: This is a realistic current. (b) IDENTIFY: The current density is J = nqv d SET UP: Solve for the drift velocity: v d = J/nq EXECUTE: Since most laboratory wire is copper, we use the value of n for copper, giving 62 d (1.50 10 A/m ) v /[(8.5 10 28 el/m 3 )(1.60 19 10 C) = 1.1 4 10 m/s = 0.11 mm/s EVALUATE: This is a typical drift velocity for ordinary currents and wires. 25.16. IDENTIFY: Apply L R A and solve for L . SET UP: 2 /4 AD , where 0.462 mm D . EXECUTE: 32 8 (1.00 )( 4)(0.462 10 m) 9.75 m. 1.72 10 m RA L EVALUATE: The resistance is proportional to the length of the wire. 25.24. IDENTIFY: Apply L R A and V IR . SET UP: 2 Ar EXECUTE: 42 7 (4.50 V) (6.54 10 m) 1.37 10 m. (17.6 A)(2.50 m) RA VA L IL EVALUATE: Our result for shows that the wire is made of a metal with resistivity greater than that of good metallic conductors such as copper and aluminum.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 2

25 - CURRENT RESISTANCE AND ELECTROMOTIVE FORCE 25 25.4(a...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online