Miami Museum of Science-Psychrometer

Make a Sling Psychrometer

A psychrometer measures the amount of relative humidity in the air. Relative humidity is the amount of moisture in the airİdivided byİthe maximum amount the air can hold.İThe higher the relative humidity is, the more likely it is to rain.

Materials

2 centigrade thermometers
tape
wet gauze
rubber band
fan
table, below

Instructions

TAPE the two thermometers to the surface of a table with the numbers facing up and the liquid filled ends sticking over the edge of the table about 2.5 cm (1 inch).
Using the rubber band, TIE the wet gauze around the liquid filled end of one thermometer.
BLOW the fan on the thermomters until the temperature stops falling.
WRITE DOWN the temperature on both thermometers.
SUBTRACT the temperature on the wet thermometer from that of the dry one.
LOOK at the table below. FIND the dry thermometer temperature on the left and FOLLOW it to the right. FIND the difference between the two temperatures on the top, and FOLLOW it down. The number where the row and column intersect is the relative humidity.

Can you use your psychrometer to predict a storm?

Relative Humidity Table (in percent)

Dry Bulb Dry Bulb Minus Wet Bulb (degrees celsius)

°C	1	2	3	4	5	6	7	8	9	10
10	88	77	66	55	44	34	24	15	6
11	89	78	67	56	46	36	27	18	9
12	89	78	68	58	48	39	29	21	12
13	89	79	69	59	50	41	32	22	15	7
14	90	79	70	60	51	42	34	25	18	10
15	90	81	71	61	53	44	36	27	20	13
16	90	81	71	63	54	46	38	30	23	15
17	90	81	72	64	55	47	40	32	25	18
18	91	82	73	65	57	49	41	34	27	20
19	91	82	74	65	58	50	43	36	29	22
20	91	83	74	67	59	53	46	39	32	26
21	91	83	75	67	60	53	46	39	32	26
22	91	83	76	68	61	54	47	40	34	28
23	92	84	76	69	62	55	48	42	36	30
24	92	84	77	69	62	56	49	43	37	31
25	92	84	77	70	63	57	50	44	39	33


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°C	1	2	3	4	5	6	7	8	9	10
10	88	77	66	55	44	34	24	15	6
11	89	78	67	56	46	36	27	18	9
12	89	78	68	58	48	39	29	21	12
13	89	79	69	59	50	41	32	22	15	7
14	90	79	70	60	51	42	34	25	18	10
15	90	81	71	61	53	44	36	27	20	13
16	90	81	71	63	54	46	38	30	23	15
17	90	81	72	64	55	47	40	32	25	18
18	91	82	73	65	57	49	41	34	27	20
19	91	82	74	65	58	50	43	36	29	22
20	91	83	74	67	59	53	46	39	32	26
21	91	83	75	67	60	53	46	39	32	26
22	91	83	76	68	61	54	47	40	34	28
23	92	84	76	69	62	55	48	42	36	30
24	92	84	77	69	62	56	49	43	37	31
25	92	84	77	70	63	57	50	44	39	33

°C	1	2	3	4	5	6	7	8	9	10
10	88	77	66	55	44	34	24	15	6
11	89	78	67	56	46	36	27	18	9
12	89	78	68	58	48	39	29	21	12
13	89	79	69	59	50	41	32	22	15	7
14	90	79	70	60	51	42	34	25	18	10
15	90	81	71	61	53	44	36	27	20	13
16	90	81	71	63	54	46	38	30	23	15
17	90	81	72	64	55	47	40	32	25	18
18	91	82	73	65	57	49	41	34	27	20
19	91	82	74	65	58	50	43	36	29	22
20	91	83	74	67	59	53	46	39	32	26
21	91	83	75	67	60	53	46	39	32	26
22	91	83	76	68	61	54	47	40	34	28
23	92	84	76	69	62	55	48	42	36	30
24	92	84	77	69	62	56	49	43	37	31
25	92	84	77	70	63	57	50	44	39	33

°C	1	2	3	4	5	6	7	8	9	10
10	88	77	66	55	44	34	24	15	6
11	89	78	67	56	46	36	27	18	9
12	89	78	68	58	48	39	29	21	12
13	89	79	69	59	50	41	32	22	15	7
14	90	79	70	60	51	42	34	25	18	10
15	90	81	71	61	53	44	36	27	20	13
16	90	81	71	63	54	46	38	30	23	15
17	90	81	72	64	55	47	40	32	25	18
18	91	82	73	65	57	49	41	34	27	20
19	91	82	74	65	58	50	43	36	29	22
20	91	83	74	67	59	53	46	39	32	26
21	91	83	75	67	60	53	46	39	32	26
22	91	83	76	68	61	54	47	40	34	28
23	92	84	76	69	62	55	48	42	36	30
24	92	84	77	69	62	56	49	43	37	31
25	92	84	77	70	63	57	50	44	39	33