Does EMF change with resistance?

Does EMF change with resistance?

A cell can be thought of as a source of electromotive force (EMF) with a resistor connected in series . When a load resistance is connected, current flows through the cell and a voltage develops across the internal resistance. Voltage is a measure of energy, and energy is always conserved.

Is EMF independent of resistance?

By definition the emf is independent of both internal and external resistance, temperature, current, etc. Real cells do not necessarily behave like this. They get depleted, so the emf decreases over time.

Does external resistance affect EMF?

The emf of the cell is the electrical potential (voltage) developed within the cell due to electro-chemical reactions. It is ideally independent of the external resistance of a circuit and the current drawn. The voltage across the terminals of the cell, VT, is not.

How does changing the resistance affect the reading on the voltmeter?

Although the resistance of the voltmeter in parallel with R lowers the equivalent resistance and increases the current from the battery, it has no influence on the voltage across R being measured.

Does internal resistance remain constant?

As current decreasesd, voltage across the internal resistance of the cell, Ir, decreased (using V=IR), because internal resistance should remain constant. Therefore voltage across the terminals increased (as less is wasted across the internal resistor).

Can EMF be greater than the potential difference?

The emf of a cell is greater than terminal voltage because the potential difference between the two terminals is not connected to any of the circuit. If it connects to the circuit then the voltage is automatically reduced because of the internal resistance.

What is difference between emf and internal resistance?

The potential difference across the poles of a cell when no current is being taken from it is called the electromotive force (EMF) of the cell. If the external resistance is R and the internal resistance is r, the total resistance of the circuit is R+r, so that the current that flows is E/(R+r).

What is difference between internal resistance and external resistance?

internal resistance is the rsisitance offered by the electrolyte to the flow of electrons. external resistance is the resistance offered to the flow of electricity in the external circuit.

Does a voltmeter add resistance?

An ideal voltmeter has infinite resistance. Too low of an internal resistance in a voltmeter will adversely affect the circuit being measured. Vacuum tube voltmeters (VTVMs), transistor voltmeters, and potentiometric circuits are all means of minimizing the load placed on a measured circuit.

When does induced EMF depend on resistance of circuit?

Although Faraday’s law has no mention of resistance there may be cases when the induced emf may be dependent on the resistance of a circuit in which the emf is induced. If an induced emf produces an induced current that current will try and oppose the change producing the induced emf (Lenz).

What does EMF stand for in electromotive force?

They also possess internal resistances. Incidentally, a pure voltage source is usually referred to as an emf (which stands for electromotive force ). Of course, emf is measured in units of volts. A battery can be modeled as an emf connected in series with a resistor , which represents its internal resistance.

How is the emf of a cell determined?

The EMF of the cell can be determined by measuring the voltage across the cell using a voltmeter and the current in the circuit using an ammeter for various resistances. We can then set up a circuit to determine EMF as shown below.

When does the voltage exceed the internal resistance?

Emf and Internal Resistance. In fact, the voltage only equals the emf when the current is negligibly small. The current draw from the battery cannot normally exceed the critical value.