解：$(1)I_{ }=\frac {U_{ }}{R_{1 }+R_{2 }}=\frac {{ 12 }\ \text {V}}{{ 24 }Ω+{ 36 }Ω}={ 0.2 }\ \text {A}$
$(2)P_{1 }=I_{ }^2R_{ 1 }=({ 0.2 }\ \text {A})^2×{ 24 }Ω={0.96 }\ \text {W}$
$(3)P_{ }=U_{ }I_{ }={ 12 }\ \text{V}×{ 0.2}\ \text{A}={ 2.4 }\ \text{W}$
