DECLARE SUB cartel (ni!, nt!)

DECLARE SUB grilla (ni!, nt!)

DECLARE SUB curva (ni, nt, cod$)

COLOR 15

ni = 1: nt = 1.52

CLS

LOCATE 7, 1

PRINT " PROGRAM 'FRESNELF'"

PRINT

PRINT

PRINT "Plots the reflectivity"; : COLOR 14: PRINT " TE "; : COLOR 15

PRINT "and"; : COLOR 11: PRINT " TM "; : COLOR 15: PRINT "of an interfase between two media of indices"

PRINT "ni and nt with light coming in one and opposite direction from 0 to 90 degrees."

PRINT "There are shown the Brewster angle ab, the critical angle ac and the"

PRINT "reflectivity in normal incidence Rn. The default values are those of Fig. 1.7."

PRINT "To finish put ni or nt = 0."

DO: LOOP WHILE INKEY$ = ""

SCREEN 12

DO

CLS

PRINT "ni="; ni;

INPUT a$: IF a$ <> "" THEN ni = VAL(a$)

IF ni = 0 THEN END

PRINT "nt="; nt;

INPUT a$: IF a$ <> "" THEN nt = VAL(a$)

IF nt = 0 THEN END

CLS

CALL cartel(ni, nt)

CALL grilla(ni, nt)

cod$ = "te"

CALL curva(ni, nt, cod$)

cod$ = "tm"

CALL curva(ni, nt, cod$)

DO: LOOP WHILE INKEY$ = ""

SWAP ni, nt

CLS

CALL cartel(ni, nt)

CALL grilla(ni, nt)

cod$ = "te"

CALL curva(ni, nt, cod$)

cod$ = "tm"

CALL curva(ni, nt, cod$)

DO: LOOP WHILE INKEY$ = ""

LOOP

SUB cartel (ni, nt)

pi = 4 * ATN(1)

LOCATE 2, 2: PRINT "ni ="; ni

LOCATE 3, 2: PRINT "nt ="; nt

Rn = ((ni - nt) / (ni + nt)) ^ 2

LOCATE 4, 2

PRINT "Rn ="; INT(100000 * Rn + .5) / 1000; "%"

x = nt / ni

abr = ATN(x)

abg = abr * 180 / pi

LOCATE 5, 2

PRINT "ab ="; INT(100 * abg + .5) / 100

xl = 640 * abg / 90

LINE (xl, 432)-(xl, 479)

IF x < 1 THEN

acr = ATN((x / SQR(1 - x ^ 2)))

acg = acr * 180 / pi

LOCATE 6, 2

PRINT "ac ="; INT(100 * acg + .5) / 100

END IF

END SUB

SUB curva (ni, nt, cod$)

pi = 4 * ATN(1)

FOR i = 0 TO pi / 2 STEP pi / 640

seni = SIN(i)

cosi = COS(i)

z = (ni * seni / nt) ^ 2

cost = SQR(ABS(1 - z))

IF z >= 1 THEN cost = 0

SELECT CASE cod$

CASE "tm"

r = ((nt * cosi - ni * cost) / (nt * cosi + ni * cost)) ^ 2

col = 11

CASE "te"

r = ((ni * cosi - nt * cost) / (ni * cosi + nt * cost)) ^ 2

col = 14

END SELECT

x = 1280 * i / pi

y = 479 * (1 - r)

IF i = 0 THEN PSET (x, y)

LINE -(x, y), col

NEXT i

END SUB

SUB grilla (ni, nt)

FOR y = 0 TO 479 STEP 48

LINE (0, y)-(640, y), 8

NEXT y

FOR y = 0 TO 479 STEP 4.8

LINE (0, y)-(5, y), 8

LINE (634, y)-(639, y), 8

NEXT y

LINE (0, 479)-(639, 479), 8

FOR x = 0 TO 639 STEP 71

LINE (x, 0)-(x, 479), 8

NEXT x

FOR x = 0 TO 639 STEP 7.1

LINE (x, 0)-(x, 5), 8

LINE (x, 474)-(x, 479), 8

NEXT x

END SUB