Question

有一個開口向上豎直放置的底面積為S=1 dm²的氣缸(如圖所示),用活塞密封2 g氦氣.初始溫度為0 ℃、外面大氣壓強為p=10 N/cm².已知氦氣在體積不變的條件下比熱容為c_V=3.1 J/（g·℃）,在壓強不變的條件下比熱容為c_p=5.2 J/(g·℃),活塞重G=50 N,活塞與筒壁摩擦不計.現對氦氣加熱,使活塞緩慢升高(保持氦氣的壓強不變),當活塞升高Δh=4 cm時停止加熱.

(1)在加熱過程中外面大氣對活塞做了多少功?活塞對氦氣做了多少功?

(2)在加熱過程中氦氣共吸收的熱量Q為多少?氦氣的溫度升高到多少攝氏度?

Answer 1

(1)W_氣=-pSΔh=-40 J                                                

    W_活塞=-p_內SΔh                                                  

    P_內=p+G/S                                                           

    W_活塞=-42 J.                                                           

(2)Q=c_pmΔT                                                              

    ΔU=c_VmΔT                                                          

    ΔU=Q+W_活塞                                                           

Q=104 J                                                              

    t₂=10 ℃.