If we double the resistance in a circuit but keep the current in it constant, the power dissipated by that circuit will

By definition, the power is equal to the product of the current high squared by the value of the resistance.
 In other words:
 P = I ^ 2 * R
 where,
 I: Current
 R: resistance
 If we double the resistance in a circuit but keep the current in it constant, then:
 P = (I ^ 2) * (2 * R)
 P = 2 * (I ^ 2 * R)
 The power increases twice.
 
 The power dissipated by that circuit will increase twice

If the heat engine is a perfect carnot cycle engine, thenefficiency = (t2-t1)/t2   where t1=temperature of cold reservoir ( ° k) = 135            t2=temperature of hot reservoir ( ° k)   = 325thereforeefficiency = (t2-t1)/t2 = (325-135)/325 = 0.5846 = 58%  note: this is the theoretical maximum efficiency of a perfect heat engine.   real-life engines do not achieve this value.