In 24 days a radioactive isotope decreases in mass from 64g to 2g. What is the half life of the radioactive material

• A. 0.75 days
• B. 2.58 days
• C. 4 days
• D. 4.80 days

An electric kettle rated 1500W boils away 0.3kg of a liquid at its boiling point every 300s. Calculate the specific latent heat of the vaporisation of the liquid

• A. 1.5 x \(10^6Jkg^-1\)
• B. 1.35 x \(10^6Jkg^-1\)
• C. 1.5 x \(10^5Jkg^-1\)
• D. 4.5 x \(10^2Jkg^-1\)

The nucleon number and the proton number of a neutral atom of an element are 238 and 92 respectively. What is the number of neutrons in the atom?

• A. 330
• B. 238
• C. 146
• D. 119

A body accelerates uniformly from rest at 2ms^?2. Calculate the velocity after traveling 9m

• A. 36ms^?1
• B. 18ms^?1
• C. 6ms^?1
• D. 4.5ms^?1

The ice and steam points on a mercury in glass thermometer are found to be 90mm apart. What temperature is recorded in degree Celsius when the length of the mercury thread is 33.6mm above the ice point mark?

• A. 33.6°C
• B. 35.0°C
• C. 37.3°C
• D. 52.7°C

The wave function of a metal is 8.0 x \(10^{-19}\)J. Calculate the wavelength of its threshold frequency. (Speed of light in a vacuum = 3 x \(10^8ms^{-1}, Planck's constant = 6.6 \times 10^{-34}\)Js)

• A.0.8 x \(10^{-7}\)m
• B.1 x \(10^{-7}\)m
• C.2.3 x \(10^{-7}\)m
• D.3.8 x \(10^{-7}\)m

(a) The specific heat capacity of copper is 400 \(JKg^{-1}K^{-1}\) means that 400 J of heat energy is required to raise (or lower) the temperature of 1 kg of a piece of copper by 1 kelvin.

(b) Experiment to determine the specific heat capacity of copper using a copper ball. The piece of copper ball is suspended by a thread and placed in a beaker of boiling water. While the temperature of the copper is being raised to boiling point of water, a copper calorimeter is half filled with water. The initial temperature of the water is measured and recorded and the hot copper ball is lifted by the thread and transferred to the calorimeter when the water has reached boiling point. The calorimeter cover is put on, the mixture is well stirred and the final steady temperature read from the themometer. The copper ball is weighed either before or after the experiment. The result is tabulated as shown below.

Mass of copper ball - m (kg)

Temperature of boiling water - \(\theta\) (K)

Mass of copper calorimeter - \(m_{c}\) (kg)

Mass of calorimeter + water - \(m_{x}\) (kg)

Mass of water \((m_{x} - m_{c})\) - \(m_{w}\) (kg)

Specific heat capacity - C \((Jkg^{-1} K^{-1})\)

Initial temperature of water = \(\theta_{w}\) (K)

Final temperature of water = \(\theta_{f}\) (K)

Using Heat lost by copper ball = Heat gained by calorimeter + Heat gained by water

\(mc(\theta - \theta_{f}) = m_{c} c (\theta_{f} - \theta_{w}) + m_{w} c_{w} (\theta_{f} - \theta_{w})\)

\(c = \frac{m_{w} c_{w} (\theta_{f} - \theta_{w})}{m (\theta - \theta_{f}) - m_{c} (\theta_{f} - \theta_{w})}\)

Precautions: (i) The copper ball should be transferred quickly into the calorimeter without splashing. (ii) Just before transfer, the copper should be shaken slightly to remove adhering hot water.

(iii) Heat lost by copper ball = heat gained by copper calorimeter + Hoat gained by water.

\(m_{c} (\theta - \theta_{f}) = m c (\theta_{f} - \theta_{w}) + m_{w} c_{w} (\theta_{f} - \theta_{w})\)

\(20 \times 0.4 \times (200 - \theta_{f}) = 60 \times 0.4 \times (\theta_{f} - 30) + 50 \times 4.2 \times (\theta_{f} - 30)\)

\(8(200 - \theta_{f}) = 24(\theta_{f} - 30) + 210 (\theta_{f} - 30)\)

\(\theta_{f} = \frac{8620}{242} = 35.6K\)

A cell of e.m.f. 1.5V and internal resistance of 2.5Ω is connected in series with an ammeter of resistance 0.5W and a resistor of resistance of 7.0Ω. Calculate the current in the circuit.

• A. 0.15A
• B. 0.20A
• C. 2.10A
• D. 3A

A lamp marked 100W, 250V is lit for 10 hours. If it operates normally and 1KWh of electrical energy costs 2k, what is the cost of lighting the lamp?

• A. 1k
• B. 2k
• C. 5k
• D. 10k

Water boils at a lower temperature when heated at the top of a mountain than at sea-level because at the top of the mountain the

• A. saturation vapour pressure of water is higher than at sea-level
• B. sun adds more heat to the water
• C. temperature is lower than at sea- level
• D. pressure of the atmosphere is lower