A brass telephone wire has essentially no sag between poles 35.0 m apart on a cold day when the temperature is -20.0°C. How much longer is the wire on a summer day when the temperature is 35.0°C? If we change the kind of wire copper, how much longer is it during summer? Which is longer?
"\\Delta l_b=\\alpha_b l_0\\Delta t=3.6~cm,"
"\\Delta l_c=\\alpha_c l_0\\Delta t=3.2~cm."
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