RI 2021 Y6 H2 Phy T3 CT Soln

© Raffles Institution [Turn over 2021 July Common Test H2 Physics Solutions 1 C The other three statements are equivalent to the statement “The molecules of the two systems have the same root -mean-square speed”. In general, root -mean-square speed is different from mean speed. 2 C In equilibrium, the two ideal gases have the same temperature: 11 1 22 2 ,pV n RT p V n RT = = Taking ratio, 11 1 1 12 2 22 22 1 2.0 0.50 1.0 1.13.0 0.30 0.90 pV n p nV pV n p nV ×=⇒= = = = × 3 D A process is adiabatic if there is no heat transfer into or from the gas. All four processes involve the expansion of an ideal gas. So, work done by the gas is positive, or the work done on the system is negative. If there is not heat absorbed into the system (as in an adiabatic process), the internal energy of the system has to decrease (ΔU = W + Q, with W negative and Q = 0, implies that ΔU must be negative). Hence, the temperature of the system has to decrease (since U ∝ T for an ideal gas). 4 A Option B: As a counter example, a system undergoing phase transitions such as melting or boiling has an increasing internal energy at a fixed temperature. Options C and D: A system with higher temperature can have less internal energy than another at a lower temperature by having less mass, and vice versa. 5 D 222 00 0 6 2 12 44 4 QqF rddπε πε πε ×= = = After contact, both charges have +2.0 μC charge. The electric force is repulsive. 1 22 0 0 2 2 16 4 344 2 FF dd πεπε ×= = =   6 B ( ) ( ) ( ) 3 6 3 6 35 3 40 30 10 405.0 10 30 10 40work done 5.0 10 12 10 8.0 10 J30 10 E VE d F qE − − − − −− − ∆= =∆ × = = ×  × = × −× = − × ×

2 © Raffles Institution 7 B 0000 0 10 4 32electric potential 22224444 2222 4321 42 2 5.09 10 Q QQQ Q Q πε πε πε πε πε −−=+++                −− + +=  = −× 8 D D 2 4 19 28 3 20 0.0021 4.5 10 1.6 104 8.02 10 m nAv q n n π −− − = = × × ×× ×× = × I 9 C There is work done when current flows through internal resistance r and a potential difference across it. Hence, the terminal p.d. decreases. 10 B The effect of the increase in the number of charge carriers is large than the effect of an increase in the frequency of collision between lattice ions and charge carriers. Hence, the ratio V I decreases and the curve gets steeper. 11 A Power dissipated, 2VP R= Since the resistors are identical, P ∝ V2 Y and Z are connected in parallel. Hence, VX : VY : VZ or VX 2 : VY 2 : VZ 2 2 : 1 : 1 or 4 : 1 : 1 Power dissipated across X = 1 24 4.0 W6 ×= 12 A Direction of electric force on electrons is upwards. Therefore, the direction of magnetic force on the electrons has to be downwards (magnetic field is into paper). Direction of electric force on alpha particles is downwards. Direction of magnetic force on alpha particles is upwards. When magnitude of B i