Physics-lab-presentation.ppt
- 1. Section-B18 Group-8 MD. Mahfuzur Rahman (23-54003-3) MD Tanjid Hasan Rafid(23-54001-3) Tasfia Islam Raisha(23-55710-3) Lameya Nourin(23-55707-3) Tahmida Zurka(23-53996-3) Ashfaq Rahman(23-55706-3) Physics Lab Presentation
- 2. To determine the temperature co-efficient of resistance of the material of a wire.
- 3. Temperature coefficient of resistance is the property of the material of a substance. It is the measure of change in electrical resistance of any substance per degree of temperature change.
- 4. This graph shows the changes in resistances of a conductor and a semiconductor with temperature. For conductor the resistance increases linearly and for semiconductor the resistance decreases exponentially with the temperature.
- 5. For a conductor the resistance increases with increase of temperature, as the figure 1 shows. If R1 is the resistance of a conductor at temperature θ1 and at a higher temperature θ2 the resistance raises to R2, then we can write: Here, 𝜶 = temperature coefficient of the material of the conductor, ∆𝑅 = change in resistance due to the change in temperature ∆𝜃.
- 6. Thus we define the temperature coefficient of resistance of a substance as the change in resistance per unit resistance for unit change in temperature. Also, we find the unit of 𝛼 as per degree Celsius We can then calculate the temperature coefficient of resistance of its material by using the equation. The unknown resistance can be determined by a meter bridge that works with the Wheatstone bridge principle.
- 8. In the meter bridge circuit as in figure 3, for the null deflection in the galvanometer we get
- 9. According to above equation, if we know the length of the balance point, l and the resistance, R we can determine the unknown resistance S.
- 10. Power supply, meter bridge, galvanometer, jockey, resistance box, coil of conducting wire, commutator, thermometer, beaker, water, electric heater.
- 12. The figure 4 apparatus was constructed. Firstly, the coil of wire was connected in the left gap (𝐺1 ) and was kept inside the beaker at room temperature. 𝜃1 from the thermometer was noted. The resistance box was connected to the right gap (𝐺2 ) of the meter bridge. The direction of the flow of electricity through the circuit was changed through closing of the knobs in different positions of the commutator. Different resistances (example: 5,7,9 Ohms) were taken from the resistance box and the balance positions on the meter bridge were found. The measurements for the reverse current were also found. The connections of the resistance box and the coil of wire were swapped on the meter bridge gaps.
- 13. The direct and reverse current readings for the same resistances (example: 5,7,9 Ohms) were also taken. The temperature inside the beaker was raised by pouring hot water. The high temperature (𝜃2 ) was noted from the thermometer. The balance points for the same resistances (example: 5,7,9 Ohms) were again found for direct and reverse currents as well as for connection of the coil of wire to the right and left gaps of the meter bridge. The value of the unknown resistance was found for left and right gaps. The temperature coefficient (α) was also calculated. .
- 17. The connections should be neat, tight and clean. There shouldn’t be any loops in the wire The plugs should be tightly connected in the resistance box. The wire might be of non-uniform diameter. To avoid the error of parallax, the set square should be used to note the null point. To maintain stable condition, temperature chamber should be used