2006 - JAMB Physics Past Questions and Answers - page 4

An n- type semi conductor is usually formed by dopping the semi conductor(a four valent element)with a five valent

element.(arsenic and antimony)

Refraction index (n)= (Real depth)/App. depth

For 80 m Real depth: (4)/3 = (80)/App. depth

App. dept = (80 x 3)/4 = 60 m

For 60 m real depth; (4)/3 = (60)/ App. depth

App. depth = (60 x 3)/4 = 45 m

∴change in App. depth = 60 -45 = 15 m

In a closed tube, the fundamental note occurs when the length of the tube l = (λ)/4,

the first over tone occurs when the length of the tube l = (3)/4λ.

λ = (4)/3 l = (4)/3 x (33)/T = 44 cm

The least distance of distinct vision required = 25 cm.

∴ for the person to see an object clearly at 25 cm from the eye, the image must be formed at 75 cm on the same side of lens, at his near point.

∴ U = 25 cm; V = -75 cm (image should be virtual)

thus (1)/f = (1)/v +(1)/u

= (1)/75 + (1)/25

=(-1 + 3)/75 = (2)/75

∴f = (75)/2 = 37.50

Work done = product of the charge Q, and the p.d V.

(i)/e work done = Q.V = 600 x 10^-6 x 3.0 x 10^-3 = 1.8 J.

R = (1)/a, P = (R.a)/1 = (0.1 x 3.14)/2 (10^-3/2)³

∴ P = (0.1 x 3.14 x 10^-6)/2 x 4

= 0.3925 x 10^-7 OR -3.930 X 10^-8 Ωm