There is no such coin. All US nickels except the famous "war nickels" of 1942-45 have been made of an alloy of 75% copper and 25% nickel.
If your coin appears to be copper, it could be plated or it could be discolored from exposure to chemicals or heat.
If you're absolutely certain it's not made of cupronickel it should be evaluated by an experienced dealer or appraiser who can check its composition, but it's extremely unlikely to be anything other than an ordinary 5¢ coin.
The "P" is the mintmark of the Philadelphia Mint. All U.S. coins from 1980 to 2012 made at this mint have a "P" mintmark. It's just a nickel, spend it.
You have to inspect your coin carefully. If it has a P or D mint mark, it's made of copper-nickel, not silver and is only worth 25¢. If it has an S mint mark and a copper-colored edge it's a copper-nickel proof coin worth maybe $2 to $10 depending on its quality. If it's in a holder labelled "Prestige Proof", then it IS a 90% silver coin. These were made for collectors and sell for $3 to $12 depending on quality and which state is depicted.
You have to inspect your coin carefully. If it has a P or D mint mark, it's made of copper-nickel, not silver and is only worth 25¢. If it has an S mint mark and a copper-colored edge it's a copper-nickel proof coin worth maybe $2 to $11 depending on its quality. If it's in a holder labelled "Prestige Proof", then it IS a silver coin, but it's not solid silver. U.S. silver coins have at least 10% copper in them. These were made for collectors and sell for $3 to $15 depending on quality and which state is depicted.
First you have to determine whether the coin is silver or copper-nickel. All circulating half dollars dated 1971 and later are made of copper-nickel, just like dimes and quarters. If your coin has a P or D above the date, it's a circulation strike so it's only worth 50 cents. Special silver halves have been made for sale to collectors, but those carry an "S" above the date and are in special holders with the words Prestige Proof on them. If that's what you have, please see the Related Question for more information.
All circulation 1971 and later halves are made of copper-nickel, not silver, so they have no added value if you found it in change. A nice uncirculated 1981-P half might bring $1 to $8 depending on quality. A 1981-D would be $1 to $12.
That depends on which version you have. If there is no mintmark, then it's made of copper and nickel, worth maybe 50 cents in decent condition. If there is a large letter P on the back (above Monticello), then it's a silver war nickel, worth a dollar or two.
A little under $2.
Around $1.50.
The coin is made from a alloy of silver, copper and manganese
Copper-nickel - 5 g - ø 21.4 mm
From mid-1942 to the end of 1945, U.S. nickels were made of silver, copper, and manganese because the metal nickel was needed for the war effort. As of 06/2009, these coins are worth about $1, depending on condition.
A 1944-P Jefferson nickel in very fine condition (VF20) is worth: $2.00; if its mint state is MS60, the value rises to; $16.00.
There are two different Jefferson nickels dated 1942. One is made from 35% silver with a large "P" or "S" mintmark on the reverse over Monticello. This is a War Nickel that's worth about $1.00 in circulated condition. The other is a common copper-nickel coin that in circulated condition is really only worth face value.
Around $1.50.
1p and 2p decimal coins never contained nickel. They were made of bronze until September 1992 when the composition was changed to copper-plated steel. Some 2p coins were struck in bronze during 1998 as well.
The P mint mark was only used on the back of nickels dated 1942 to 1945. If that's what you have it's a so-called "war nickel" made of copper, manganese, and silver as a means of conserving nickel for the war effort. They sell for about 80-90 cents in circulated condition. Nickels dated 1980 and later may have a P or D on the front, but they're only worth 5 cents.
The value of a Jefferson nickel with a p mint mark will vary depending on the year and the condition of the coin itself. A person should have the coin appraised for an accurate value.