Resistance Thermometers

Q.

At room temperature (27.0 °C) the resistance of a heating element is 100 Ω. What is the temperature of the element if the resistance is found to be 117 Ω, given that the temperature coefficient of the material of the resistor is

Q. The actual value of resistance $R$, shown in the figure is $30\Omega$. This is measured in an experiment as shown using the standard formula $R=\frac{V}{I}$, where $V$ and $I$ are the reading of the voltmeter and ammeter, respectively. If the measured value of $R$ is $5\%$ less, then the internal resistance of the voltmeter is

1. $600\Omega$
2. $570\Omega$
3. $35\Omega$
4. $350\Omega$

Q.

A platinum resistance thermometer reads $0^{\circ }$ when its resistance is 80 $\Omega$ and ${100}^{\circ }$ when its resistance is 90 $\Omega$. Find the temperature at the platinum scale at which the resistance is 86 $\Omega$

Q.

State the use of a bimetallic strip in the thermostat.

Q.

A resistance thermometer reads R = 20.0 $\Omega$, 27.5 $\Omega$, and 50.0 $\Omega$ at the ice point ($0^{\circ }C$), the steam point (${100}^{\circ }C$) and the zinc point (${420}^{\circ }C$) respectively. Assuming that the resistance varies with temperature as $R_{\theta }=R_0(1+\alpha \theta +\beta {\theta }^2)$, find the values of $R_0,\alpha$ and $\beta$. Here $\theta$ represents the temperature on Celsius scale.

Q.

The resistance of a resistance thermometer has values 2.71 and 3.70 ohm at ${10}^{\circ }Cand{100}^{\circ }C$. The temperature at which the resistance is 3.26 ohm is

1. ${40}^{\circ }C$

2. ${50}^{\circ }C$

3. ${60}^{\circ }C$

4. ${70}^{\circ }C$

Q.

The electrical resistance in ohms of a certain thermometer varies with temperature according to the approximate law:

R = R_o [1 + α (T – T_o)]

The resistance is 101.6 Ω at the triple-point of water 273.16 K, and 165.5 Ω at the normal melting point of lead (600.5 K). What is the temperature when the resistance is 123.4 Ω?

Q.

Aheating element using nichrome connected to a 230 V supply draws an initial current of 3.2 A which settles after a few seconds toa steady value of 2.8 A. What is the steady temperature of the heating element if the room temperature is 27.0 °C? Temperature coefficient of resistance of nichrome averaged over the temperature range involved is 1.70 × 10⁻⁴ °C ⁻¹.

Q. The constant A in the Richardson−Dushman equation for tungsten is 60 × 10⁴ A m⁻² K⁻². The work function of tungsten is 4.5 eV. A tungsten cathode with a surface area 2.0 × 10⁻⁵ m² is heated by a 24 W electric heater. In steady state, the heat radiated by the heater and the cathode equals the energy input by the heater and the temperature becomes constant. Assuming that the cathode radiates like a blackbody, calculate the saturation current due to thermions. Take Stefan's Constant = 6 × 10⁻⁸ W m⁻² K⁻¹. Assume that the thermions take only a small fraction of the heat supplied.

Q. 1.which type of material(wire) is used in resistance thermometer?
2.which thermometer is more sensitive? mercury or gas
3.which range of temp. can you measure using platinum resistance thermometer?

Q. Consider the following statements A and B and identify the correct answer
A : Thermistors can have only -ve temperature coefficient of resistors.
B : Thermistors with -ve temperature coefficients of resistance are used as resistance thermometers to measure low temperature of the order of 10K

1. 1) both A and B are true
2. 3) A is true and B is false
3. 2) both A and B are false
4. 4) A is false, but B is true

Q. The resistances of a platinum resistance thermometer at the ice point, the steam point and the boiling point of sulphur are 2.50, 3.50 and 6.50 $\Omega$ respectively. Find the boiling point (${}^{o}C$) of sulphur on the platinum scale. The ice point and the steam point measure $0^{\circ }C$ and ${100}^{\circ }C$ respectively.

Q. We cannot use mercury thermometer at low temperatures because:

1. Glass might break down at low temperature.
2. Mercury freezes at low temperatures.
3. At low temperatures mercury becomes transparent and it becomes difficult to take the readings.
4. Heat does not flow from the body whose measurement we are taking with the thermometer.

Q. A capacitor of capacitance 12.0 μF is connected to a battery of emf 6.00 V and internal resistance 1.00 Ω through resistanceless leads. 12.0 μs after the connections are made, what will be (a) the current in the circuit (b) the power delivered by the battery (c) the power dissipated in heat and (d) the rate at which the energy stored in the capacitor is increasing?

Q. The coil of an electric bulb takes 40 watts to start glowing. If more than 40 W are supplied, 60% of the extra power is converted into light and the remaining into heat. The bulb consumes 100 W at 220 V. Find the percentage drop in the light intensity at a point if the supply voltage changes from 220 V to 200 V.

Q. The resistance of the coil of an ammeter is R. The shunt required to increase its range n-fold should have a resistance

1. $\frac{R}{n}$
2. $\frac{R}{n-1}$
3. $\text{nR}$
4. $\frac{R}{n+1}$

Q. No other thermometer is as suitable as a platinum resistance thermometer to measure temperatures in the entire range of

1. $-{50}^{\circ }C$ to $+{350}^{\circ }C$
2. $-{200}^{\circ }C$ to $+{600}^{\circ }C$
3. $0^{\circ }C$ to $+{100}^{\circ }C$
4. ${100}^{\circ }C$ to $+{1500}^{\circ }C$

Q. Resistance of a resistor at temperature $t$ ${}^o\text{C}$ is $R_t=R_0(1+\alpha t+\beta t^2)$, where $R_0$ is the resistance at $0{}^o\text{C}$. The temperature coefficient of resistance at temperature $t{}^o\text{C}$ is

1. $\frac{\alpha +2\beta t}{(1+\alpha t+\beta t^2)}$
2. $\frac{\alpha +2\beta t}{2(1+\alpha t+\beta t^2)}$
3. $\frac{(1+\alpha t+\beta t^2)}{\alpha +2\beta t}$
4. $(\alpha +2\beta t)$

Q. If I were to use measure changing temperature using a resistor, how would I do it?

1. Pass a current through the resistor and measure it. Change in current will give change in temperature.
2. Connect a battery across the resistor. The battery's supply voltage changes with temperature.
3. The resistor will change shape noticably for even small changes in temperature.
4. I'll just use a thermometer

Q. A platinum resistance thermometer reads 0° when its resistance is 80 Ω and 100° when its resistance is 90 Ω.
Find the temperature at the platinum scale at which the resistance is 86 Ω.

Q. The thermal energy developed in a current-carrying resistor is given by U = i² Rt and also by U = Vit. Should we say that U is proportional to i² or i?

Q. State whether true or false :
A gas thermometer measures temperature with the variation in pressure or volume of a gas.

1. True
2. False

Q. An LR circuit having a time constant of 50 ms is connected with an ideal battery of emf ε. find the time elapsed before (a) the current reaches half its maximum value, (b) the power dissipated in heat reaches half its maximum value and (c) the magnetic field energy stored in the circuit reaches half its maximum value.

Q. Apply the first law of thermodynamics to a resistor carrying a current i. Identify which of the quantities ∆Q, ∆U and ∆W are zero, positive and negative.

Q. The difference between ATC and AVC will be constant, because TFC is constant.

1. True
2. False

Q.

The electrical resistance in ohms of a certain thermometer varies with temperature according to the approximate law:

R = R_o [1 + α (T – T_o)]

The resistance is 101.6 Ω at the triple-point of water 273.16 K, and 165.5 Ω at the normal melting point of lead (600.5 K). What is the temperature when the resistance is 123.4 Ω?

Q. With increase of hot junction temperature in thermocouple thermo emf :

1. always increases with temperature
2. can be positive (or) negative
3. is always positive
4. first increases with temperature and then decreases with temperature

Q. A coil of resistance 100 Ω is connected across a battery of emf 6.0 V. Assume that the heat developed in the coil is used to raise its temperature. If the heat capacity of the coil is 4.0 J K⁻¹, how long will it take to raise the temperature of the coil by 15°C?

Q. Suppose the ends of the coil in the previous problem are connected to a resistance of 100 Ω. Neglecting the resistance of the coil, find the heat produced in the circuit in one minute.

Q. Shown in figure is a Post Office box. In order to calculate the value ofexternal resistance, it should be connected between :

1. B and C
2. A and D
3. C and D
4. B and D